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 $49.47   9.422%   $54.1311   $54.13   $54.15   $54.10  
  Purchase #2 $157.51   12.156%   $176.6569   $176.66   $176.65   $176.70  
  Purchase #3 $84.94   12.777%   $95.7928   $95.79   $95.80   $95.80  
  Purchase #4 $152.69   6.370%   $162.4164   $162.42   $162.40   $162.40  
  Purchase #5 $241.33   13.126%   $273.007   $273.01   $273.00   $273.00  
  Purchase #6 $36.53   4.456%   $38.1578   $38.16   $38.15   $38.20  
  Purchase #7 $119.54   11.527%   $133.3194   $133.32   $133.30   $133.30  
  7 purchase totals = $842.01       $933.4814   $933.49   $933.45   $933.50