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 $49.43   10.858%   $54.7971   $54.80   $54.80   $54.80  
  Purchase #2 $43.51   5.792%   $46.0301   $46.03   $46.05   $46.00  
  Purchase #3 $213.44   5.831%   $225.8857   $225.89   $225.90   $225.90  
  Purchase #4 $186.71   3.515%   $193.2729   $193.27   $193.25   $193.30  
  Purchase #5 $239.42   10.261%   $263.9869   $263.99   $264.00   $264.00  
  Purchase #6 $241.99   10.711%   $267.9095   $267.91   $267.90   $267.90  
  Purchase #7 $132.38   12.139%   $148.4496   $148.45   $148.45   $148.40  
  7 purchase totals = $1,106.88       $1,200.3318   $1,200.34   $1,200.35   $1,200.30