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 $189.79   11.805%   $212.1947   $212.19   $212.20   $212.20  
  Purchase #2 $102.46   12.474%   $115.2409   $115.24   $115.25   $115.20  
  Purchase #3 $104.75   6.118%   $111.1586   $111.16   $111.15   $111.20  
  Purchase #4 $65.81   11.734%   $73.5321   $73.53   $73.55   $73.50  
  Purchase #5 $54.76   13.520%   $62.1636   $62.16   $62.15   $62.20  
  Purchase #6 $26.33   7.693%   $28.3556   $28.36   $28.35   $28.40  
  Purchase #7 $81.90   6.720%   $87.4037   $87.40   $87.40   $87.40  
  7 purchase totals = $625.80       $690.0492   $690.04   $690.05   $690.10