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 $219.96   12.523%   $247.5056   $247.51   $247.50   $247.50  
  Purchase #2 $242.40   13.239%   $274.4913   $274.49   $274.50   $274.50  
  Purchase #3 $164.34   5.730%   $173.7567   $173.76   $173.75   $173.80  
  Purchase #4 $113.52   5.338%   $119.5797   $119.58   $119.60   $119.60  
  Purchase #5 $170.94   11.667%   $190.8836   $190.88   $190.90   $190.90  
  Purchase #6 $23.38   3.374%   $24.1688   $24.17   $24.15   $24.20  
  Purchase #7 $126.44   5.289%   $133.1274   $133.13   $133.15   $133.10  
  7 purchase totals = $1,060.98       $1,163.5131   $1,163.52   $1,163.55   $1,163.60