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 $51.79   5.363%   $54.5675   $54.57   $54.55   $54.60  
  Purchase #2 $188.74   3.341%   $195.0458   $195.05   $195.05   $195.00  
  Purchase #3 $200.90   4.217%   $209.372   $209.37   $209.35   $209.40  
  Purchase #4 $238.37   13.725%   $271.0863   $271.09   $271.10   $271.10  
  Purchase #5 $110.92   11.860%   $124.0751   $124.08   $124.10   $124.10  
  Purchase #6 $201.34   12.627%   $226.7632   $226.76   $226.75   $226.80  
  Purchase #7 $82.84   8.849%   $90.1705   $90.17   $90.15   $90.20  
  7 purchase totals = $1,074.90       $1,171.0804   $1,171.09   $1,171.05   $1,171.20