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 $217.26   13.335%   $246.2316   $246.23   $246.25   $246.20  
  Purchase #2 $64.95   7.304%   $69.6939   $69.69   $69.70   $69.70  
  Purchase #3 $170.52   7.326%   $183.0123   $183.01   $183.00   $183.00  
  Purchase #4 $153.63   10.697%   $170.0638   $170.06   $170.05   $170.10  
  Purchase #5 $238.52   10.148%   $262.725   $262.73   $262.75   $262.70  
  Purchase #6 $210.60   9.661%   $230.9461   $230.95   $230.95   $230.90  
  Purchase #7 $86.37   6.256%   $91.7733   $91.77   $91.75   $91.80  
  7 purchase totals = $1,141.85       $1,254.4460   $1,254.44   $1,254.45   $1,254.40