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 $220.59   11.445%   $245.8365   $245.84   $245.85   $245.80  
  Purchase #2 $240.48   5.482%   $253.6631   $253.66   $253.65   $253.70  
  Purchase #3 $93.83   6.775%   $100.187   $100.19   $100.20   $100.20  
  Purchase #4 $73.78   7.646%   $79.4212   $79.42   $79.40   $79.40  
  Purchase #5 $246.88   3.253%   $254.911   $254.91   $254.90   $254.90  
  Purchase #6 $232.72   6.361%   $247.5233   $247.52   $247.50   $247.50  
  Purchase #7 $46.29   11.152%   $51.4523   $51.45   $51.45   $51.50  
  7 purchase totals = $1,154.57       $1,232.9944   $1,232.99   $1,232.95   $1,233.00