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 $227.60   7.118%   $243.8006   $243.80   $243.80   $243.80  
  Purchase #2 $243.63   5.102%   $256.06   $256.06   $256.05   $256.10  
  Purchase #3 $37.86   3.529%   $39.1961   $39.20   $39.20   $39.20  
  Purchase #4 $168.28   5.450%   $177.4513   $177.45   $177.45   $177.50  
  Purchase #5 $41.95   9.784%   $46.0544   $46.05   $46.05   $46.10  
  Purchase #6 $168.93   13.356%   $191.4923   $191.49   $191.50   $191.50  
  Purchase #7 $58.60   10.501%   $64.7536   $64.75   $64.75   $64.80  
  7 purchase totals = $946.85       $1,018.8083   $1,018.80   $1,018.80   $1,019.00