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 $178.52   11.840%   $199.6568   $199.66   $199.65   $199.70  
  Purchase #2 $65.82   10.439%   $72.6909   $72.69   $72.70   $72.70  
  Purchase #3 $126.75   12.744%   $142.903   $142.90   $142.90   $142.90  
  Purchase #4 $246.25   10.150%   $271.2444   $271.24   $271.25   $271.20  
  Purchase #5 $71.51   4.420%   $74.6707   $74.67   $74.65   $74.70  
  Purchase #6 $139.77   9.473%   $153.0104   $153.01   $153.00   $153.00  
  Purchase #7 $26.30   7.184%   $28.1894   $28.19   $28.20   $28.20  
  7 purchase totals = $854.92       $942.3656   $942.36   $942.35   $942.40