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 $215.75   12.303%   $242.2937   $242.29   $242.30   $242.30  
  Purchase #2 $110.38   6.260%   $117.2898   $117.29   $117.30   $117.30  
  Purchase #3 $110.54   12.779%   $124.6659   $124.67   $124.65   $124.70  
  Purchase #4 $192.64   11.412%   $214.6241   $214.62   $214.60   $214.60  
  Purchase #5 $214.56   7.567%   $230.7958   $230.80   $230.80   $230.80  
  Purchase #6 $201.40   12.441%   $226.4562   $226.46   $226.45   $226.50  
  Purchase #7 $61.26   13.829%   $69.7316   $69.73   $69.75   $69.70  
  7 purchase totals = $1,106.53       $1,225.8571   $1,225.86   $1,225.85   $1,225.90