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 $206.53   11.765%   $230.8283   $230.83   $230.85   $230.80  
  Purchase #2 $208.95   12.125%   $234.2852   $234.29   $234.30   $234.30  
  Purchase #3 $161.28   4.696%   $168.8537   $168.85   $168.85   $168.90  
  Purchase #4 $236.81   4.869%   $248.3403   $248.34   $248.35   $248.30  
  Purchase #5 $29.71   12.728%   $33.4915   $33.49   $33.50   $33.50  
  Purchase #6 $224.33   8.540%   $243.4878   $243.49   $243.50   $243.50  
  Purchase #7 $150.80   5.870%   $159.652   $159.65   $159.65   $159.70  
  7 purchase totals = $1,218.41       $1,318.9388   $1,318.94   $1,319.00   $1,319.00