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 $150.35   13.859%   $171.187   $171.19   $171.20   $171.20  
  Purchase #2 $174.37   8.367%   $188.9595   $188.96   $188.95   $189.00  
  Purchase #3 $47.97   13.206%   $54.3049   $54.30   $54.30   $54.30  
  Purchase #4 $21.76   10.868%   $24.1249   $24.12   $24.10   $24.10  
  Purchase #5 $128.31   11.293%   $142.8   $142.80   $142.80   $142.80  
  Purchase #6 $229.62   13.473%   $260.5567   $260.56   $260.55   $260.60  
  Purchase #7 $187.56   4.280%   $195.5876   $195.59   $195.60   $195.60  
  7 purchase totals = $939.94       $1,037.5206   $1,037.52   $1,037.50   $1,037.60