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 $43.55   6.228%   $46.2623   $46.26   $46.25   $46.30  
  Purchase #2 $55.48   4.565%   $58.0127   $58.01   $58.00   $58.00  
  Purchase #3 $96.31   6.164%   $102.2465   $102.25   $102.25   $102.20  
  Purchase #4 $159.27   6.413%   $169.484   $169.48   $169.50   $169.50  
  Purchase #5 $202.60   5.306%   $213.35   $213.35   $213.35   $213.40  
  Purchase #6 $139.65   13.547%   $158.5684   $158.57   $158.55   $158.60  
  Purchase #7 $213.64   8.489%   $231.7759   $231.78   $231.80   $231.80  
  7 purchase totals = $910.50       $979.6998   $979.70   $979.70   $979.80