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 $34.62   5.871%   $36.6525   $36.65   $36.65   $36.70  
  Purchase #2 $134.71   13.243%   $152.5496   $152.55   $152.55   $152.50  
  Purchase #3 $141.88   4.117%   $147.7212   $147.72   $147.70   $147.70  
  Purchase #4 $222.47   6.333%   $236.559   $236.56   $236.55   $236.60  
  Purchase #5 $54.53   13.473%   $61.8768   $61.88   $61.90   $61.90  
  Purchase #6 $99.91   9.368%   $109.2696   $109.27   $109.25   $109.30  
  Purchase #7 $204.93   13.573%   $232.7451   $232.75   $232.75   $232.70  
  7 purchase totals = $893.05       $977.3738   $977.38   $977.35   $977.40