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 $62.87   9.655%   $68.9401   $68.94   $68.95   $68.90  
  Purchase #2 $202.41   12.250%   $227.2052   $227.21   $227.20   $227.20  
  Purchase #3 $205.60   9.828%   $225.8064   $225.81   $225.80   $225.80  
  Purchase #4 $190.50   11.187%   $211.8112   $211.81   $211.80   $211.80  
  Purchase #5 $181.34   3.213%   $187.1665   $187.17   $187.15   $187.20  
  Purchase #6 $22.63   11.645%   $25.2653   $25.27   $25.25   $25.30  
  Purchase #7 $78.68   12.481%   $88.5001   $88.50   $88.50   $88.50  
  7 purchase totals = $944.03       $1,034.6948   $1,034.71   $1,034.65   $1,034.70