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 $14.75   6.267%   $15.6744   $15.67   $15.65   $15.70  
  Purchase #2 $224.32   10.133%   $247.0503   $247.05   $247.05   $247.10  
  Purchase #3 $74.64   3.188%   $77.0195   $77.02   $77.00   $77.00  
  Purchase #4 $125.26   10.263%   $138.1154   $138.12   $138.10   $138.10  
  Purchase #5 $247.33   5.396%   $260.6759   $260.68   $260.70   $260.70  
  Purchase #6 $215.70   13.119%   $243.9977   $244.00   $244.00   $244.00  
  Purchase #7 $50.72   5.412%   $53.465   $53.47   $53.45   $53.50  
  7 purchase totals = $952.72       $1,035.9982   $1,036.01   $1,035.95   $1,036.10