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 $23.35   5.239%   $24.5733   $24.57   $24.55   $24.60  
  Purchase #2 $223.97   10.374%   $247.2046   $247.20   $247.20   $247.20  
  Purchase #3 $127.25   3.216%   $131.3424   $131.34   $131.35   $131.30  
  Purchase #4 $241.50   6.834%   $258.0041   $258.00   $258.00   $258.00  
  Purchase #5 $235.31   8.587%   $255.5161   $255.52   $255.50   $255.50  
  Purchase #6 $222.49   9.811%   $244.3185   $244.32   $244.30   $244.30  
  Purchase #7 $42.36   11.679%   $47.3072   $47.31   $47.30   $47.30  
  7 purchase totals = $1,116.23       $1,208.2662   $1,208.26   $1,208.20   $1,208.20