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 $197.25   13.699%   $224.2713   $224.27   $224.25   $224.30  
  Purchase #2 $103.85   4.322%   $108.3384   $108.34   $108.35   $108.30  
  Purchase #3 $226.84   5.838%   $240.0829   $240.08   $240.10   $240.10  
  Purchase #4 $143.53   4.663%   $150.2228   $150.22   $150.20   $150.20  
  Purchase #5 $133.57   11.178%   $148.5005   $148.50   $148.50   $148.50  
  Purchase #6 $223.59   5.321%   $235.4872   $235.49   $235.50   $235.50  
  Purchase #7 $15.67   11.170%   $17.4203   $17.42   $17.40   $17.40  
  7 purchase totals = $1,044.30       $1,124.3234   $1,124.32   $1,124.30   $1,124.30