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 $38.33   13.713%   $43.5862   $43.59   $43.60   $43.60  
  Purchase #2 $53.44   9.273%   $58.3955   $58.40   $58.40   $58.40  
  Purchase #3 $234.62   6.501%   $249.8726   $249.87   $249.85   $249.90  
  Purchase #4 $227.80   6.351%   $242.2676   $242.27   $242.25   $242.30  
  Purchase #5 $75.55   12.146%   $84.7263   $84.73   $84.75   $84.70  
  Purchase #6 $238.56   7.769%   $257.0937   $257.09   $257.10   $257.10  
  Purchase #7 $173.71   9.371%   $189.9884   $189.99   $190.00   $190.00  
  7 purchase totals = $1,042.01       $1,125.9303   $1,125.94   $1,125.95   $1,126.00