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 $210.49   12.758%   $237.3443   $237.34   $237.35   $237.30  
  Purchase #2 $189.85   9.623%   $208.1193   $208.12   $208.10   $208.10  
  Purchase #3 $151.36   11.864%   $169.3174   $169.32   $169.30   $169.30  
  Purchase #4 $217.34   12.207%   $243.8707   $243.87   $243.85   $243.90  
  Purchase #5 $69.99   9.273%   $76.4802   $76.48   $76.50   $76.50  
  Purchase #6 $202.71   4.293%   $211.4123   $211.41   $211.40   $211.40  
  Purchase #7 $144.42   8.308%   $156.4184   $156.42   $156.40   $156.40  
  7 purchase totals = $1,186.16       $1,302.9626   $1,302.96   $1,302.90   $1,302.90