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 $229.70   12.203%   $257.7303   $257.73   $257.75   $257.70  
  Purchase #2 $155.94   13.718%   $177.3318   $177.33   $177.35   $177.30  
  Purchase #3 $13.99   4.300%   $14.5916   $14.59   $14.60   $14.60  
  Purchase #4 $166.84   12.344%   $187.4347   $187.43   $187.45   $187.40  
  Purchase #5 $60.61   12.834%   $68.3887   $68.39   $68.40   $68.40  
  Purchase #6 $205.58   8.813%   $223.6978   $223.70   $223.70   $223.70  
  Purchase #7 $139.99   9.533%   $153.3352   $153.34   $153.35   $153.30  
  7 purchase totals = $972.65       $1,082.5101   $1,082.51   $1,082.60   $1,082.40