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 $246.53   10.321%   $271.9744   $271.97   $271.95   $272.00  
  Purchase #2 $88.82   5.377%   $93.5959   $93.60   $93.60   $93.60  
  Purchase #3 $223.95   5.631%   $236.5606   $236.56   $236.55   $236.60  
  Purchase #4 $93.47   9.359%   $102.2179   $102.22   $102.20   $102.20  
  Purchase #5 $122.55   7.396%   $131.6138   $131.61   $131.60   $131.60  
  Purchase #6 $28.28   12.685%   $31.8673   $31.87   $31.85   $31.90  
  Purchase #7 $91.67   8.708%   $99.6526   $99.65   $99.65   $99.70  
  7 purchase totals = $895.27       $967.4825   $967.48   $967.40   $967.60