Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.78   12.258%   $107.5207   $107.52   $107.50   $107.50  
  Purchase #2 $186.62   10.190%   $205.6366   $205.64   $205.65   $205.60  
  Purchase #3 $220.64   12.496%   $248.2112   $248.21   $248.20   $248.20  
  Purchase #4 $112.26   3.643%   $116.3496   $116.35   $116.35   $116.30  
  Purchase #5 $225.86   9.319%   $246.9079   $246.91   $246.90   $246.90  
  Purchase #6 $213.97   3.711%   $221.9104   $221.91   $221.90   $221.90  
  Purchase #7 $110.28   10.336%   $121.6785   $121.68   $121.70   $121.70  
  7 purchase totals = $1,165.41       $1,268.2149   $1,268.22   $1,268.20   $1,268.10