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 $211.87   6.319%   $225.2581   $225.26   $225.25   $225.30  
  Purchase #2 $143.29   6.742%   $152.9506   $152.95   $152.95   $153.00  
  Purchase #3 $71.97   9.723%   $78.9676   $78.97   $78.95   $79.00  
  Purchase #4 $22.36   9.597%   $24.5059   $24.51   $24.50   $24.50  
  Purchase #5 $80.35   4.350%   $83.8452   $83.85   $83.85   $83.80  
  Purchase #6 $216.32   6.119%   $229.5566   $229.56   $229.55   $229.60  
  Purchase #7 $142.63   4.670%   $149.2908   $149.29   $149.30   $149.30  
  7 purchase totals = $888.79       $944.3748   $944.39   $944.35   $944.50