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 $126.55   10.512%   $139.8529   $139.85   $139.85   $139.90  
  Purchase #2 $207.30   3.152%   $213.8341   $213.83   $213.85   $213.80  
  Purchase #3 $133.30   8.590%   $144.7505   $144.75   $144.75   $144.80  
  Purchase #4 $231.35   12.639%   $260.5903   $260.59   $260.60   $260.60  
  Purchase #5 $99.66   4.686%   $104.3301   $104.33   $104.35   $104.30  
  Purchase #6 $167.52   5.269%   $176.3466   $176.35   $176.35   $176.30  
  Purchase #7 $30.58   13.185%   $34.612   $34.61   $34.60   $34.60  
  7 purchase totals = $996.26       $1,074.3165   $1,074.31   $1,074.35   $1,074.30