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 $42.41   11.306%   $47.2049   $47.20   $47.20   $47.20  
  Purchase #2 $65.47   12.479%   $73.64   $73.64   $73.65   $73.60  
  Purchase #3 $187.52   11.803%   $209.653   $209.65   $209.65   $209.70  
  Purchase #4 $241.86   5.659%   $255.5469   $255.55   $255.55   $255.50  
  Purchase #5 $165.51   6.122%   $175.6425   $175.64   $175.65   $175.60  
  Purchase #6 $60.62   6.148%   $64.3469   $64.35   $64.35   $64.30  
  Purchase #7 $104.41   4.818%   $109.4405   $109.44   $109.45   $109.40  
  7 purchase totals = $867.80       $935.4747   $935.47   $935.50   $935.30