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 $184.59   4.789%   $193.43   $193.43   $193.45   $193.40  
  Purchase #2 $54.77   13.629%   $62.2346   $62.23   $62.25   $62.20  
  Purchase #3 $159.90   7.860%   $172.4681   $172.47   $172.45   $172.50  
  Purchase #4 $247.94   4.651%   $259.4717   $259.47   $259.45   $259.50  
  Purchase #5 $163.66   6.546%   $174.3732   $174.37   $174.35   $174.40  
  Purchase #6 $118.40   11.853%   $132.434   $132.43   $132.45   $132.40  
  Purchase #7 $193.87   13.141%   $219.3465   $219.35   $219.35   $219.30  
  7 purchase totals = $1,123.13       $1,213.7581   $1,213.75   $1,213.75   $1,213.70