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 $64.96   6.382%   $69.1057   $69.11   $69.10   $69.10  
  Purchase #2 $149.54   7.670%   $161.0097   $161.01   $161.00   $161.00  
  Purchase #3 $194.38   9.210%   $212.2824   $212.28   $212.30   $212.30  
  Purchase #4 $176.37   4.797%   $184.8305   $184.83   $184.85   $184.80  
  Purchase #5 $149.95   12.845%   $169.2111   $169.21   $169.20   $169.20  
  Purchase #6 $245.98   5.120%   $258.5742   $258.57   $258.55   $258.60  
  Purchase #7 $137.77   9.588%   $150.9794   $150.98   $151.00   $151.00  
  7 purchase totals = $1,118.95       $1,205.9930   $1,205.99   $1,206.00   $1,206.00