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 $215.52   13.510%   $244.6368   $244.64   $244.65   $244.60  
  Purchase #2 $157.29   10.245%   $173.4044   $173.40   $173.40   $173.40  
  Purchase #3 $220.96   8.156%   $238.9815   $238.98   $239.00   $239.00  
  Purchase #4 $94.56   8.660%   $102.7489   $102.75   $102.75   $102.70  
  Purchase #5 $200.79   9.626%   $220.118   $220.12   $220.10   $220.10  
  Purchase #6 $155.94   10.683%   $172.5991   $172.60   $172.60   $172.60  
  Purchase #7 $96.55   10.720%   $106.9002   $106.90   $106.90   $106.90  
  7 purchase totals = $1,141.61       $1,259.3889   $1,259.39   $1,259.40   $1,259.30