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 $118.66   3.371%   $122.66   $122.66   $122.65   $122.70  
  Purchase #2 $184.48   8.359%   $199.9007   $199.90   $199.90   $199.90  
  Purchase #3 $162.94   4.514%   $170.2951   $170.30   $170.30   $170.30  
  Purchase #4 $182.98   11.633%   $204.2661   $204.27   $204.25   $204.30  
  Purchase #5 $217.36   6.224%   $230.8885   $230.89   $230.90   $230.90  
  Purchase #6 $21.60   5.866%   $22.8671   $22.87   $22.85   $22.90  
  Purchase #7 $194.42   13.212%   $220.1068   $220.11   $220.10   $220.10  
  7 purchase totals = $1,082.44       $1,170.9843   $1,171.00   $1,170.95   $1,171.10