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 $61.92   6.763%   $66.1076   $66.11   $66.10   $66.10  
  Purchase #2 $225.82   7.630%   $243.0501   $243.05   $243.05   $243.10  
  Purchase #3 $167.85   3.859%   $174.3273   $174.33   $174.35   $174.30  
  Purchase #4 $75.52   12.229%   $84.7553   $84.76   $84.75   $84.80  
  Purchase #5 $105.50   9.462%   $115.4824   $115.48   $115.50   $115.50  
  Purchase #6 $81.70   4.757%   $85.5865   $85.59   $85.60   $85.60  
  Purchase #7 $60.85   3.153%   $62.7686   $62.77   $62.75   $62.80  
  7 purchase totals = $779.16       $832.0778   $832.09   $832.10   $832.20