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 $193.68   10.629%   $214.2662   $214.27   $214.25   $214.30  
  Purchase #2 $64.71   10.296%   $71.3725   $71.37   $71.35   $71.40  
  Purchase #3 $141.46   8.717%   $153.7911   $153.79   $153.80   $153.80  
  Purchase #4 $41.82   6.571%   $44.568   $44.57   $44.55   $44.60  
  Purchase #5 $230.78   7.237%   $247.4815   $247.48   $247.50   $247.50  
  Purchase #6 $179.37   10.577%   $198.342   $198.34   $198.35   $198.30  
  Purchase #7 $25.45   11.303%   $28.3266   $28.33   $28.35   $28.30  
  7 purchase totals = $877.27       $958.1479   $958.15   $958.15   $958.20