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 $215.55   7.548%   $231.8197   $231.82   $231.80   $231.80  
  Purchase #2 $126.36   3.117%   $130.2986   $130.30   $130.30   $130.30  
  Purchase #3 $98.60   12.489%   $110.9142   $110.91   $110.90   $110.90  
  Purchase #4 $70.75   8.867%   $77.0234   $77.02   $77.00   $77.00  
  Purchase #5 $33.52   13.260%   $37.9648   $37.96   $37.95   $38.00  
  Purchase #6 $237.46   6.643%   $253.2345   $253.23   $253.25   $253.20  
  Purchase #7 $176.52   3.446%   $182.6029   $182.60   $182.60   $182.60  
  7 purchase totals = $958.76       $1,023.8581   $1,023.84   $1,023.80   $1,023.80