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 $85.75   8.107%   $92.7018   $92.70   $92.70   $92.70  
  Purchase #2 $52.44   10.167%   $57.7716   $57.77   $57.75   $57.80  
  Purchase #3 $152.61   13.587%   $173.3451   $173.35   $173.35   $173.30  
  Purchase #4 $213.27   12.131%   $239.1418   $239.14   $239.15   $239.10  
  Purchase #5 $158.83   6.475%   $169.1142   $169.11   $169.10   $169.10  
  Purchase #6 $96.29   5.559%   $101.6428   $101.64   $101.65   $101.60  
  Purchase #7 $199.79   9.403%   $218.5763   $218.58   $218.60   $218.60  
  7 purchase totals = $958.98       $1,052.2936   $1,052.29   $1,052.30   $1,052.20