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 $33.74   6.297%   $35.8646   $35.86   $35.85   $35.90  
  Purchase #2 $190.97   4.379%   $199.3326   $199.33   $199.35   $199.30  
  Purchase #3 $118.95   5.259%   $125.2056   $125.21   $125.20   $125.20  
  Purchase #4 $211.52   3.763%   $219.4795   $219.48   $219.50   $219.50  
  Purchase #5 $245.64   9.242%   $268.342   $268.34   $268.35   $268.30  
  Purchase #6 $242.34   13.510%   $275.0801   $275.08   $275.10   $275.10  
  Purchase #7 $90.74   8.821%   $98.7442   $98.74   $98.75   $98.70  
  7 purchase totals = $1,133.90       $1,222.0486   $1,222.04   $1,222.10   $1,222.00