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 $81.90   3.393%   $84.6789   $84.68   $84.70   $84.70  
  Purchase #2 $126.31   5.344%   $133.06   $133.06   $133.05   $133.10  
  Purchase #3 $176.37   11.551%   $196.7425   $196.74   $196.75   $196.70  
  Purchase #4 $242.25   10.846%   $268.5244   $268.52   $268.50   $268.50  
  Purchase #5 $9.55   3.482%   $9.8825   $9.88   $9.90   $9.90  
  Purchase #6 $91.35   3.408%   $94.4632   $94.46   $94.45   $94.50  
  Purchase #7 $7.41   7.802%   $7.9881   $7.99   $8.00   $8.00  
  7 purchase totals = $735.14       $795.3396   $795.33   $795.35   $795.40