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 $228.82   7.468%   $245.9083   $245.91   $245.90   $245.90  
  Purchase #2 $232.83   4.151%   $242.4948   $242.49   $242.50   $242.50  
  Purchase #3 $47.93   7.772%   $51.6551   $51.66   $51.65   $51.70  
  Purchase #4 $213.42   12.816%   $240.7719   $240.77   $240.75   $240.80  
  Purchase #5 $103.49   4.383%   $108.026   $108.03   $108.05   $108.00  
  Purchase #6 $248.89   9.802%   $273.2862   $273.29   $273.30   $273.30  
  Purchase #7 $247.53   7.267%   $265.518   $265.52   $265.50   $265.50  
  7 purchase totals = $1,322.91       $1,427.6603   $1,427.67   $1,427.65   $1,427.70