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 $134.78   8.770%   $146.6002   $146.60   $146.60   $146.60  
  Purchase #2 $174.73   9.692%   $191.6648   $191.66   $191.65   $191.70  
  Purchase #3 $88.38   10.162%   $97.3612   $97.36   $97.35   $97.40  
  Purchase #4 $190.98   11.146%   $212.2666   $212.27   $212.25   $212.30  
  Purchase #5 $184.78   10.248%   $203.7163   $203.72   $203.70   $203.70  
  Purchase #6 $188.25   9.558%   $206.2429   $206.24   $206.25   $206.20  
  Purchase #7 $21.80   4.560%   $22.7941   $22.79   $22.80   $22.80  
  7 purchase totals = $983.70       $1,080.6461   $1,080.64   $1,080.60   $1,080.70