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 $196.49   3.816%   $203.9881   $203.99   $204.00   $204.00  
  Purchase #2 $35.34   3.408%   $36.5444   $36.54   $36.55   $36.50  
  Purchase #3 $186.42   3.844%   $193.586   $193.59   $193.60   $193.60  
  Purchase #4 $229.33   7.603%   $246.766   $246.77   $246.75   $246.80  
  Purchase #5 $184.37   13.758%   $209.7356   $209.74   $209.75   $209.70  
  Purchase #6 $191.65   6.429%   $203.9712   $203.97   $203.95   $204.00  
  Purchase #7 $41.67   8.266%   $45.1144   $45.11   $45.10   $45.10  
  7 purchase totals = $1,065.27       $1,139.7057   $1,139.71   $1,139.70   $1,139.70