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 $235.79   5.111%   $247.8412   $247.84   $247.85   $247.80  
  Purchase #2 $239.33   5.706%   $252.9862   $252.99   $253.00   $253.00  
  Purchase #3 $31.29   13.794%   $35.6061   $35.61   $35.60   $35.60  
  Purchase #4 $115.93   6.499%   $123.4643   $123.46   $123.45   $123.50  
  Purchase #5 $101.44   10.175%   $111.7615   $111.76   $111.75   $111.80  
  Purchase #6 $169.43   7.563%   $182.244   $182.24   $182.25   $182.20  
  Purchase #7 $62.90   7.552%   $67.6502   $67.65   $67.65   $67.70  
  7 purchase totals = $956.11       $1,021.5535   $1,021.55   $1,021.55   $1,021.60