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 $73.61   7.119%   $78.8503   $78.85   $78.85   $78.90  
  Purchase #2 $169.31   4.605%   $177.1067   $177.11   $177.10   $177.10  
  Purchase #3 $147.36   5.518%   $155.4913   $155.49   $155.50   $155.50  
  Purchase #4 $75.92   11.856%   $84.9211   $84.92   $84.90   $84.90  
  Purchase #5 $62.84   12.453%   $70.6655   $70.67   $70.65   $70.70  
  Purchase #6 $193.51   3.506%   $200.2945   $200.29   $200.30   $200.30  
  Purchase #7 $61.63   10.562%   $68.1394   $68.14   $68.15   $68.10  
  7 purchase totals = $784.18       $835.4688   $835.47   $835.45   $835.50