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 $74.63   12.476%   $83.9408   $83.94   $83.95   $83.90  
  Purchase #2 $207.50   13.107%   $234.697   $234.70   $234.70   $234.70  
  Purchase #3 $248.47   9.250%   $271.4535   $271.45   $271.45   $271.50  
  Purchase #4 $27.42   3.815%   $28.4661   $28.47   $28.45   $28.50  
  Purchase #5 $219.83   7.399%   $236.0952   $236.10   $236.10   $236.10  
  Purchase #6 $155.70   11.448%   $173.5245   $173.52   $173.50   $173.50  
  Purchase #7 $23.63   10.465%   $26.1029   $26.10   $26.10   $26.10  
  7 purchase totals = $957.18       $1,054.2800   $1,054.28   $1,054.25   $1,054.30