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 $171.68   7.623%   $184.7672   $184.77   $184.75   $184.80  
  Purchase #2 $23.97   8.629%   $26.0384   $26.04   $26.05   $26.00  
  Purchase #3 $66.53   5.439%   $70.1486   $70.15   $70.15   $70.10  
  Purchase #4 $117.64   5.265%   $123.8337   $123.83   $123.85   $123.80  
  Purchase #5 $149.53   13.811%   $170.1816   $170.18   $170.20   $170.20  
  Purchase #6 $183.72   6.652%   $195.9411   $195.94   $195.95   $195.90  
  Purchase #7 $88.88   9.415%   $97.2481   $97.25   $97.25   $97.20  
  7 purchase totals = $801.95       $868.1587   $868.16   $868.20   $868.00