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 $225.78   8.440%   $244.8358   $244.84   $244.85   $244.80  
  Purchase #2 $68.75   7.520%   $73.92   $73.92   $73.90   $73.90  
  Purchase #3 $25.25   9.499%   $27.6485   $27.65   $27.65   $27.60  
  Purchase #4 $172.74   11.870%   $193.2442   $193.24   $193.25   $193.20  
  Purchase #5 $177.28   9.172%   $193.5401   $193.54   $193.55   $193.50  
  Purchase #6 $138.88   3.782%   $144.1324   $144.13   $144.15   $144.10  
  Purchase #7 $132.79   7.797%   $143.1436   $143.14   $143.15   $143.10  
  7 purchase totals = $941.47       $1,020.4646   $1,020.46   $1,020.50   $1,020.20