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 $58.35   11.268%   $64.9249   $64.92   $64.90   $64.90  
  Purchase #2 $68.28   5.759%   $72.2122   $72.21   $72.20   $72.20  
  Purchase #3 $109.26   8.661%   $118.723   $118.72   $118.70   $118.70  
  Purchase #4 $57.52   5.586%   $60.7331   $60.73   $60.75   $60.70  
  Purchase #5 $164.49   4.274%   $171.5203   $171.52   $171.50   $171.50  
  Purchase #6 $114.63   3.129%   $118.2168   $118.22   $118.20   $118.20  
  Purchase #7 $169.33   3.131%   $174.6317   $174.63   $174.65   $174.60  
  7 purchase totals = $741.86       $780.9620   $780.95   $780.90   $780.80