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 $193.70   11.772%   $216.5024   $216.50   $216.50   $216.50  
  Purchase #2 $174.58   11.511%   $194.6759   $194.68   $194.70   $194.70  
  Purchase #3 $24.39   12.125%   $27.3473   $27.35   $27.35   $27.30  
  Purchase #4 $93.99   11.568%   $104.8628   $104.86   $104.85   $104.90  
  Purchase #5 $206.87   9.544%   $226.6137   $226.61   $226.60   $226.60  
  Purchase #6 $21.50   12.469%   $24.1808   $24.18   $24.20   $24.20  
  Purchase #7 $229.26   3.698%   $237.738   $237.74   $237.75   $237.70  
  7 purchase totals = $944.29       $1,031.9209   $1,031.92   $1,031.95   $1,031.90