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 $243.87   5.468%   $257.2048   $257.20   $257.20   $257.20  
  Purchase #2 $179.94   13.200%   $203.6921   $203.69   $203.70   $203.70  
  Purchase #3 $127.38   13.566%   $144.6604   $144.66   $144.65   $144.70  
  Purchase #4 $156.31   12.364%   $175.6362   $175.64   $175.65   $175.60  
  Purchase #5 $234.43   10.829%   $259.8164   $259.82   $259.80   $259.80  
  Purchase #6 $58.75   9.446%   $64.2995   $64.30   $64.30   $64.30  
  Purchase #7 $234.50   5.371%   $247.095   $247.10   $247.10   $247.10  
  7 purchase totals = $1,235.18       $1,352.4044   $1,352.41   $1,352.40   $1,352.40