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 $91.26   12.131%   $102.3308   $102.33   $102.35   $102.30  
  Purchase #2 $175.25   6.323%   $186.3311   $186.33   $186.35   $186.30  
  Purchase #3 $119.88   5.152%   $126.0562   $126.06   $126.05   $126.10  
  Purchase #4 $248.59   3.443%   $257.149   $257.15   $257.15   $257.10  
  Purchase #5 $213.31   7.529%   $229.3701   $229.37   $229.35   $229.40  
  Purchase #6 $222.45   6.772%   $237.5143   $237.51   $237.50   $237.50  
  Purchase #7 $89.91   8.328%   $97.3977   $97.40   $97.40   $97.40  
  7 purchase totals = $1,160.65       $1,236.1492   $1,236.15   $1,236.15   $1,236.10