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 $48.89   5.359%   $51.51   $51.51   $51.50   $51.50  
  Purchase #2 $84.69   9.499%   $92.7347   $92.73   $92.75   $92.70  
  Purchase #3 $29.54   10.587%   $32.6674   $32.67   $32.65   $32.70  
  Purchase #4 $200.37   11.282%   $222.9757   $222.98   $223.00   $223.00  
  Purchase #5 $153.49   12.205%   $172.2235   $172.22   $172.20   $172.20  
  Purchase #6 $10.66   7.361%   $11.4447   $11.44   $11.45   $11.40  
  Purchase #7 $223.31   4.523%   $233.4103   $233.41   $233.40   $233.40  
  7 purchase totals = $750.95       $816.9663   $816.96   $816.95   $816.90