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 $225.99   12.447%   $254.119   $254.12   $254.10   $254.10  
  Purchase #2 $84.84   8.656%   $92.1838   $92.18   $92.20   $92.20  
  Purchase #3 $150.89   3.357%   $155.9554   $155.96   $155.95   $156.00  
  Purchase #4 $188.85   12.743%   $212.9152   $212.92   $212.90   $212.90  
  Purchase #5 $179.97   10.172%   $198.2765   $198.28   $198.30   $198.30  
  Purchase #6 $56.84   12.600%   $64.0018   $64.00   $64.00   $64.00  
  Purchase #7 $151.84   5.487%   $160.1715   $160.17   $160.15   $160.20  
  7 purchase totals = $1,039.22       $1,137.6232   $1,137.63   $1,137.60   $1,137.70