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 $235.34   12.492%   $264.7387   $264.74   $264.75   $264.70  
  Purchase #2 $98.35   10.494%   $108.6708   $108.67   $108.65   $108.70  
  Purchase #3 $45.76   10.319%   $50.482   $50.48   $50.50   $50.50  
  Purchase #4 $29.59   5.685%   $31.2722   $31.27   $31.25   $31.30  
  Purchase #5 $187.61   7.582%   $201.8346   $201.83   $201.85   $201.80  
  Purchase #6 $232.92   10.171%   $256.6103   $256.61   $256.60   $256.60  
  Purchase #7 $177.67   7.420%   $190.8531   $190.85   $190.85   $190.90  
  7 purchase totals = $1,007.24       $1,104.4617   $1,104.45   $1,104.45   $1,104.50