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 $75.52   13.137%   $85.4411   $85.44   $85.45   $85.40  
  Purchase #2 $213.59   12.253%   $239.7612   $239.76   $239.75   $239.80  
  Purchase #3 $178.52   12.490%   $200.8171   $200.82   $200.80   $200.80  
  Purchase #4 $96.37   7.363%   $103.4657   $103.47   $103.45   $103.50  
  Purchase #5 $113.25   11.142%   $125.8683   $125.87   $125.85   $125.90  
  Purchase #6 $5.63   10.185%   $6.2034   $6.20   $6.20   $6.20  
  Purchase #7 $243.28   5.786%   $257.3562   $257.36   $257.35   $257.40  
  7 purchase totals = $926.16       $1,018.9130   $1,018.92   $1,018.85   $1,019.00