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 $219.67   10.479%   $242.6892   $242.69   $242.70   $242.70  
  Purchase #2 $222.43   9.683%   $243.9679   $243.97   $243.95   $244.00  
  Purchase #3 $154.51   9.130%   $168.6168   $168.62   $168.60   $168.60  
  Purchase #4 $67.68   13.679%   $76.9379   $76.94   $76.95   $76.90  
  Purchase #5 $178.64   8.446%   $193.7279   $193.73   $193.75   $193.70  
  Purchase #6 $216.95   6.524%   $231.1038   $231.10   $231.10   $231.10  
  Purchase #7 $11.54   13.312%   $13.0762   $13.08   $13.10   $13.10  
  7 purchase totals = $1,071.42       $1,170.1197   $1,170.13   $1,170.15   $1,170.10