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 $84.48   11.218%   $93.957   $93.96   $93.95   $94.00  
  Purchase #2 $14.91   10.426%   $16.4645   $16.46   $16.45   $16.50  
  Purchase #3 $23.71   8.753%   $25.7853   $25.79   $25.80   $25.80  
  Purchase #4 $228.49   4.865%   $239.606   $239.61   $239.60   $239.60  
  Purchase #5 $187.66   10.314%   $207.0153   $207.02   $207.00   $207.00  
  Purchase #6 $5.27   6.335%   $5.6039   $5.60   $5.60   $5.60  
  Purchase #7 $144.57   4.482%   $151.0496   $151.05   $151.05   $151.00  
  7 purchase totals = $689.09       $739.4816   $739.49   $739.45   $739.50