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 $84.81   10.588%   $93.7897   $93.79   $93.80   $93.80  
  Purchase #2 $61.27   9.123%   $66.8597   $66.86   $66.85   $66.90  
  Purchase #3 $214.43   7.789%   $231.132   $231.13   $231.15   $231.10  
  Purchase #4 $124.89   5.283%   $131.4879   $131.49   $131.50   $131.50  
  Purchase #5 $69.78   10.753%   $77.2834   $77.28   $77.30   $77.30  
  Purchase #6 $222.89   11.596%   $248.7363   $248.74   $248.75   $248.70  
  Purchase #7 $123.78   10.554%   $136.8437   $136.84   $136.85   $136.80  
  7 purchase totals = $901.85       $986.1327   $986.13   $986.20   $986.10