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 $232.48   5.808%   $245.9824   $245.98   $246.00   $246.00  
  Purchase #2 $209.97   13.442%   $238.1942   $238.19   $238.20   $238.20  
  Purchase #3 $140.35   5.473%   $148.0314   $148.03   $148.05   $148.00  
  Purchase #4 $56.57   9.693%   $62.0533   $62.05   $62.05   $62.10  
  Purchase #5 $153.29   11.723%   $171.2602   $171.26   $171.25   $171.30  
  Purchase #6 $34.41   12.215%   $38.6132   $38.61   $38.60   $38.60  
  Purchase #7 $115.57   10.416%   $127.6078   $127.61   $127.60   $127.60  
  7 purchase totals = $942.64       $1,031.7425   $1,031.73   $1,031.75   $1,031.80