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 $178.43   11.341%   $198.6657   $198.67   $198.65   $198.70  
  Purchase #2 $108.60   9.149%   $118.5358   $118.54   $118.55   $118.50  
  Purchase #3 $152.55   13.224%   $172.7232   $172.72   $172.70   $172.70  
  Purchase #4 $237.78   3.290%   $245.603   $245.60   $245.60   $245.60  
  Purchase #5 $58.90   13.135%   $66.6365   $66.64   $66.65   $66.60  
  Purchase #6 $163.70   11.184%   $182.0082   $182.01   $182.00   $182.00  
  Purchase #7 $87.46   7.534%   $94.0492   $94.05   $94.05   $94.00  
  7 purchase totals = $987.42       $1,078.2216   $1,078.23   $1,078.20   $1,078.10