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 $183.97   6.171%   $195.3228   $195.32   $195.30   $195.30  
  Purchase #2 $53.75   7.823%   $57.9549   $57.95   $57.95   $58.00  
  Purchase #3 $211.97   5.609%   $223.8594   $223.86   $223.85   $223.90  
  Purchase #4 $101.89   11.124%   $113.2242   $113.22   $113.20   $113.20  
  Purchase #5 $199.55   5.868%   $211.2596   $211.26   $211.25   $211.30  
  Purchase #6 $125.58   3.445%   $129.9062   $129.91   $129.90   $129.90  
  Purchase #7 $109.78   6.199%   $116.5853   $116.59   $116.60   $116.60  
  7 purchase totals = $986.49       $1,048.1124   $1,048.11   $1,048.05   $1,048.20