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 $53.81   11.583%   $60.0428   $60.04   $60.05   $60.00  
  Purchase #2 $16.37   6.179%   $17.3815   $17.38   $17.40   $17.40  
  Purchase #3 $130.65   5.186%   $137.4255   $137.43   $137.45   $137.40  
  Purchase #4 $193.51   13.615%   $219.8564   $219.86   $219.85   $219.90  
  Purchase #5 $233.76   13.470%   $265.2475   $265.25   $265.25   $265.20  
  Purchase #6 $242.29   6.140%   $257.1666   $257.17   $257.15   $257.20  
  Purchase #7 $149.98   8.842%   $163.2412   $163.24   $163.25   $163.20  
  7 purchase totals = $1,020.37       $1,120.3615   $1,120.37   $1,120.40   $1,120.30