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 $116.81   10.685%   $129.2911   $129.29   $129.30   $129.30  
  Purchase #2 $94.98   9.442%   $103.948   $103.95   $103.95   $103.90  
  Purchase #3 $230.69   3.764%   $239.3732   $239.37   $239.35   $239.40  
  Purchase #4 $31.56   8.762%   $34.3253   $34.33   $34.35   $34.30  
  Purchase #5 $213.63   12.655%   $240.6649   $240.66   $240.65   $240.70  
  Purchase #6 $94.43   5.459%   $99.5849   $99.58   $99.60   $99.60  
  Purchase #7 $150.59   11.255%   $167.5389   $167.54   $167.55   $167.50  
  7 purchase totals = $932.69       $1,014.7263   $1,014.72   $1,014.75   $1,014.70