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 $87.38   11.762%   $97.6576   $97.66   $97.65   $97.70  
  Purchase #2 $114.37   13.787%   $130.1382   $130.14   $130.15   $130.10  
  Purchase #3 $229.83   7.362%   $246.7501   $246.75   $246.75   $246.80  
  Purchase #4 $14.99   11.234%   $16.674   $16.67   $16.65   $16.70  
  Purchase #5 $55.86   11.417%   $62.2375   $62.24   $62.25   $62.20  
  Purchase #6 $208.31   7.286%   $223.4875   $223.49   $223.50   $223.50  
  Purchase #7 $173.37   11.740%   $193.7236   $193.72   $193.70   $193.70  
  7 purchase totals = $884.11       $970.6685   $970.67   $970.65   $970.70