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 $54.85   11.872%   $61.3618   $61.36   $61.35   $61.40  
  Purchase #2 $223.49   12.378%   $251.1536   $251.15   $251.15   $251.20  
  Purchase #3 $217.43   3.751%   $225.5858   $225.59   $225.60   $225.60  
  Purchase #4 $188.72   6.792%   $201.5379   $201.54   $201.55   $201.50  
  Purchase #5 $33.54   5.348%   $35.3337   $35.33   $35.35   $35.30  
  Purchase #6 $108.28   8.755%   $117.7599   $117.76   $117.75   $117.80  
  Purchase #7 $24.83   5.289%   $26.1433   $26.14   $26.15   $26.10  
  7 purchase totals = $851.14       $918.8760   $918.87   $918.90   $918.90