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 $221.80   11.365%   $247.0076   $247.01   $247.00   $247.00  
  Purchase #2 $61.33   5.567%   $64.7442   $64.74   $64.75   $64.70  
  Purchase #3 $70.29   4.667%   $73.5704   $73.57   $73.55   $73.60  
  Purchase #4 $120.80   13.867%   $137.5513   $137.55   $137.55   $137.60  
  Purchase #5 $121.96   9.239%   $133.2279   $133.23   $133.25   $133.20  
  Purchase #6 $246.43   12.713%   $277.7586   $277.76   $277.75   $277.80  
  Purchase #7 $104.40   4.727%   $109.335   $109.34   $109.35   $109.30  
  7 purchase totals = $947.01       $1,043.1950   $1,043.20   $1,043.20   $1,043.20