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 $48.33   8.291%   $52.337   $52.34   $52.35   $52.30  
  Purchase #2 $117.67   6.650%   $125.4951   $125.50   $125.50   $125.50  
  Purchase #3 $19.97   13.730%   $22.7119   $22.71   $22.70   $22.70  
  Purchase #4 $138.56   8.771%   $150.7131   $150.71   $150.70   $150.70  
  Purchase #5 $178.64   9.867%   $196.2664   $196.27   $196.25   $196.30  
  Purchase #6 $41.73   9.348%   $45.6309   $45.63   $45.65   $45.60  
  Purchase #7 $207.59   11.289%   $231.0248   $231.02   $231.00   $231.00  
  7 purchase totals = $752.49       $824.1792   $824.18   $824.15   $824.10