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 $51.38   6.566%   $54.7536   $54.75   $54.75   $54.80  
  Purchase #2 $219.72   8.402%   $238.1809   $238.18   $238.20   $238.20  
  Purchase #3 $207.59   8.694%   $225.6379   $225.64   $225.65   $225.60  
  Purchase #4 $146.78   10.481%   $162.164   $162.16   $162.15   $162.20  
  Purchase #5 $117.38   6.729%   $125.2785   $125.28   $125.30   $125.30  
  Purchase #6 $238.53   4.379%   $248.9752   $248.98   $249.00   $249.00  
  Purchase #7 $188.57   7.398%   $202.5204   $202.52   $202.50   $202.50  
  7 purchase totals = $1,169.95       $1,257.5105   $1,257.51   $1,257.55   $1,257.60