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 $224.48   10.187%   $247.3478   $247.35   $247.35   $247.30  
  Purchase #2 $155.42   5.488%   $163.9494   $163.95   $163.95   $163.90  
  Purchase #3 $154.38   8.515%   $167.5255   $167.53   $167.55   $167.50  
  Purchase #4 $33.79   8.751%   $36.747   $36.75   $36.75   $36.70  
  Purchase #5 $96.27   8.549%   $104.5001   $104.50   $104.50   $104.50  
  Purchase #6 $226.82   10.828%   $251.3801   $251.38   $251.40   $251.40  
  Purchase #7 $38.88   11.413%   $43.3174   $43.32   $43.30   $43.30  
  7 purchase totals = $930.04       $1,014.7673   $1,014.78   $1,014.80   $1,014.60