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 $167.77   11.860%   $187.6675   $187.67   $187.65   $187.70  
  Purchase #2 $230.73   10.374%   $254.6659   $254.67   $254.65   $254.70  
  Purchase #3 $29.62   7.701%   $31.901   $31.90   $31.90   $31.90  
  Purchase #4 $206.82   9.860%   $227.2125   $227.21   $227.20   $227.20  
  Purchase #5 $87.66   11.413%   $97.6646   $97.66   $97.65   $97.70  
  Purchase #6 $25.91   11.158%   $28.801   $28.80   $28.80   $28.80  
  Purchase #7 $20.76   5.839%   $21.9722   $21.97   $21.95   $22.00  
  7 purchase totals = $769.27       $849.8847   $849.88   $849.80   $850.00