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 $238.66   10.385%   $263.4448   $263.44   $263.45   $263.40  
  Purchase #2 $173.58   4.815%   $181.9379   $181.94   $181.95   $181.90  
  Purchase #3 $6.46   11.287%   $7.1891   $7.19   $7.20   $7.20  
  Purchase #4 $228.28   7.146%   $244.5929   $244.59   $244.60   $244.60  
  Purchase #5 $164.67   4.399%   $171.9138   $171.91   $171.90   $171.90  
  Purchase #6 $67.62   4.491%   $70.6568   $70.66   $70.65   $70.70  
  Purchase #7 $160.27   5.635%   $169.3012   $169.30   $169.30   $169.30  
  7 purchase totals = $1,039.54       $1,109.0365   $1,109.03   $1,109.05   $1,109.00