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 $201.38   3.642%   $208.7143   $208.71   $208.70   $208.70  
  Purchase #2 $107.58   6.599%   $114.6792   $114.68   $114.70   $114.70  
  Purchase #3 $63.52   6.195%   $67.4551   $67.46   $67.45   $67.50  
  Purchase #4 $165.65   9.111%   $180.7424   $180.74   $180.75   $180.70  
  Purchase #5 $234.45   13.793%   $266.7877   $266.79   $266.80   $266.80  
  Purchase #6 $71.29   6.555%   $75.9631   $75.96   $75.95   $76.00  
  Purchase #7 $85.97   9.540%   $94.1715   $94.17   $94.15   $94.20  
  7 purchase totals = $929.84       $1,008.5133   $1,008.51   $1,008.50   $1,008.60