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 $87.73   5.695%   $92.7262   $92.73   $92.75   $92.70  
  Purchase #2 $210.57   12.109%   $236.0679   $236.07   $236.05   $236.10  
  Purchase #3 $35.80   6.703%   $38.1997   $38.20   $38.20   $38.20  
  Purchase #4 $152.48   11.387%   $169.8429   $169.84   $169.85   $169.80  
  Purchase #5 $187.83   8.760%   $204.2839   $204.28   $204.30   $204.30  
  Purchase #6 $127.50   5.751%   $134.8325   $134.83   $134.85   $134.80  
  Purchase #7 $136.34   11.129%   $151.5133   $151.51   $151.50   $151.50  
  7 purchase totals = $938.25       $1,027.4664   $1,027.46   $1,027.50   $1,027.40