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 $64.93   12.716%   $73.1865   $73.19   $73.20   $73.20  
  Purchase #2 $80.29   9.769%   $88.1335   $88.13   $88.15   $88.10  
  Purchase #3 $176.51   8.763%   $191.9776   $191.98   $192.00   $192.00  
  Purchase #4 $119.51   8.264%   $129.3863   $129.39   $129.40   $129.40  
  Purchase #5 $75.55   13.268%   $85.574   $85.57   $85.55   $85.60  
  Purchase #6 $221.96   6.589%   $236.5849   $236.58   $236.60   $236.60  
  Purchase #7 $239.33   9.389%   $261.8007   $261.80   $261.80   $261.80  
  7 purchase totals = $978.08       $1,066.6435   $1,066.64   $1,066.70   $1,066.70