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 $57.36   9.368%   $62.7335   $62.73   $62.75   $62.70  
  Purchase #2 $212.42   5.379%   $223.8461   $223.85   $223.85   $223.80  
  Purchase #3 $122.73   8.356%   $132.9853   $132.99   $133.00   $133.00  
  Purchase #4 $164.59   13.518%   $186.8393   $186.84   $186.85   $186.80  
  Purchase #5 $146.46   12.140%   $164.2402   $164.24   $164.25   $164.20  
  Purchase #6 $48.75   13.275%   $55.2216   $55.22   $55.20   $55.20  
  Purchase #7 $61.29   6.685%   $65.3872   $65.39   $65.40   $65.40  
  7 purchase totals = $813.60       $891.2532   $891.26   $891.30   $891.10