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 $243.60   7.873%   $262.7786   $262.78   $262.80   $262.80  
  Purchase #2 $191.52   3.136%   $197.5261   $197.53   $197.55   $197.50  
  Purchase #3 $136.48   10.148%   $150.33   $150.33   $150.35   $150.30  
  Purchase #4 $48.93   7.397%   $52.5494   $52.55   $52.55   $52.50  
  Purchase #5 $146.43   8.459%   $158.8165   $158.82   $158.80   $158.80  
  Purchase #6 $17.45   5.728%   $18.4495   $18.45   $18.45   $18.40  
  Purchase #7 $206.92   6.442%   $220.2498   $220.25   $220.25   $220.20  
  7 purchase totals = $991.33       $1,060.6999   $1,060.71   $1,060.75   $1,060.50