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 $61.36   4.679%   $64.231   $64.23   $64.25   $64.20  
  Purchase #2 $89.54   9.222%   $97.7974   $97.80   $97.80   $97.80  
  Purchase #3 $228.37   11.435%   $254.4841   $254.48   $254.50   $254.50  
  Purchase #4 $70.31   9.753%   $77.1673   $77.17   $77.15   $77.20  
  Purchase #5 $187.88   6.596%   $200.2726   $200.27   $200.25   $200.30  
  Purchase #6 $199.71   8.256%   $216.1981   $216.20   $216.20   $216.20  
  Purchase #7 $149.41   8.309%   $161.8245   $161.82   $161.80   $161.80  
  7 purchase totals = $986.58       $1,071.9750   $1,071.97   $1,071.95   $1,072.00