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 $183.61   13.439%   $208.2853   $208.29   $208.30   $208.30  
  Purchase #2 $84.57   13.586%   $96.0597   $96.06   $96.05   $96.10  
  Purchase #3 $173.28   8.368%   $187.7801   $187.78   $187.80   $187.80  
  Purchase #4 $111.61   11.538%   $124.4876   $124.49   $124.50   $124.50  
  Purchase #5 $138.43   3.500%   $143.2751   $143.28   $143.30   $143.30  
  Purchase #6 $218.95   8.221%   $236.9499   $236.95   $236.95   $236.90  
  Purchase #7 $87.68   11.716%   $97.9526   $97.95   $97.95   $98.00  
  7 purchase totals = $998.13       $1,094.7903   $1,094.80   $1,094.85   $1,094.90