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 $51.94   9.715%   $56.986   $56.99   $57.00   $57.00  
  Purchase #2 $202.44   11.434%   $225.587   $225.59   $225.60   $225.60  
  Purchase #3 $29.80   5.857%   $31.5454   $31.55   $31.55   $31.50  
  Purchase #4 $93.51   8.322%   $101.2919   $101.29   $101.30   $101.30  
  Purchase #5 $152.69   3.166%   $157.5242   $157.52   $157.50   $157.50  
  Purchase #6 $209.34   13.247%   $237.0713   $237.07   $237.05   $237.10  
  Purchase #7 $207.84   3.143%   $214.3724   $214.37   $214.35   $214.40  
  7 purchase totals = $947.56       $1,024.3782   $1,024.38   $1,024.35   $1,024.40