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 $83.68   13.549%   $95.0178   $95.02   $95.00   $95.00  
  Purchase #2 $30.58   4.185%   $31.8598   $31.86   $31.85   $31.90  
  Purchase #3 $65.65   13.502%   $74.5141   $74.51   $74.50   $74.50  
  Purchase #4 $42.79   11.213%   $47.588   $47.59   $47.60   $47.60  
  Purchase #5 $104.30   9.196%   $113.8914   $113.89   $113.90   $113.90  
  Purchase #6 $80.75   6.733%   $86.1869   $86.19   $86.20   $86.20  
  Purchase #7 $139.97   6.390%   $148.9141   $148.91   $148.90   $148.90  
  7 purchase totals = $547.72       $597.9721   $597.97   $597.95   $598.00