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 $59.80   5.740%   $63.2325   $63.23   $63.25   $63.20  
  Purchase #2 $169.34   9.182%   $184.8888   $184.89   $184.90   $184.90  
  Purchase #3 $151.53   13.710%   $172.3048   $172.30   $172.30   $172.30  
  Purchase #4 $204.53   7.681%   $220.2399   $220.24   $220.25   $220.20  
  Purchase #5 $72.91   12.438%   $81.9785   $81.98   $82.00   $82.00  
  Purchase #6 $165.83   4.774%   $173.7467   $173.75   $173.75   $173.70  
  Purchase #7 $108.87   3.220%   $112.3756   $112.38   $112.40   $112.40  
  7 purchase totals = $932.81       $1,008.7668   $1,008.77   $1,008.85   $1,008.70