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 $14.38   8.350%   $15.5807   $15.58   $15.60   $15.60  
  Purchase #2 $53.50   12.495%   $60.1848   $60.18   $60.20   $60.20  
  Purchase #3 $212.94   9.283%   $232.7072   $232.71   $232.70   $232.70  
  Purchase #4 $124.94   12.464%   $140.5125   $140.51   $140.50   $140.50  
  Purchase #5 $172.91   5.810%   $182.9561   $182.96   $182.95   $183.00  
  Purchase #6 $233.84   9.249%   $255.4679   $255.47   $255.45   $255.50  
  Purchase #7 $156.77   10.363%   $173.0161   $173.02   $173.00   $173.00  
  7 purchase totals = $969.28       $1,060.4253   $1,060.43   $1,060.40   $1,060.50