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 $84.84   11.176%   $94.3217   $94.32   $94.30   $94.30  
  Purchase #2 $213.45   12.143%   $239.3692   $239.37   $239.35   $239.40  
  Purchase #3 $140.45   11.598%   $156.7394   $156.74   $156.75   $156.70  
  Purchase #4 $228.35   7.240%   $244.8825   $244.88   $244.90   $244.90  
  Purchase #5 $204.45   11.344%   $227.6428   $227.64   $227.65   $227.60  
  Purchase #6 $169.68   9.724%   $186.1797   $186.18   $186.20   $186.20  
  Purchase #7 $179.63   4.818%   $188.2846   $188.28   $188.30   $188.30  
  7 purchase totals = $1,220.85       $1,337.4199   $1,337.41   $1,337.45   $1,337.40