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 $244.68   11.558%   $272.9601   $272.96   $272.95   $273.00  
  Purchase #2 $152.83   9.650%   $167.5781   $167.58   $167.60   $167.60  
  Purchase #3 $14.72   11.324%   $16.3869   $16.39   $16.40   $16.40  
  Purchase #4 $130.66   12.319%   $146.756   $146.76   $146.75   $146.80  
  Purchase #5 $18.59   11.803%   $20.7842   $20.78   $20.80   $20.80  
  Purchase #6 $64.72   3.779%   $67.1658   $67.17   $67.15   $67.20  
  Purchase #7 $204.97   7.216%   $219.7606   $219.76   $219.75   $219.80  
  7 purchase totals = $831.17       $911.3917   $911.40   $911.40   $911.60