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 $172.76   11.427%   $192.5013   $192.50   $192.50   $192.50  
  Purchase #2 $84.55   6.698%   $90.2132   $90.21   $90.20   $90.20  
  Purchase #3 $175.71   12.235%   $197.2081   $197.21   $197.20   $197.20  
  Purchase #4 $243.46   11.603%   $271.7087   $271.71   $271.70   $271.70  
  Purchase #5 $32.95   6.300%   $35.0259   $35.03   $35.05   $35.00  
  Purchase #6 $149.58   11.286%   $166.4616   $166.46   $166.45   $166.50  
  Purchase #7 $80.25   3.295%   $82.8942   $82.89   $82.90   $82.90  
  7 purchase totals = $939.26       $1,036.0130   $1,036.01   $1,036.00   $1,036.00