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 $65.77   9.438%   $71.9774   $71.98   $72.00   $72.00  
  Purchase #2 $242.99   6.146%   $257.9242   $257.92   $257.90   $257.90  
  Purchase #3 $184.69   8.837%   $201.0111   $201.01   $201.00   $201.00  
  Purchase #4 $190.66   12.626%   $214.7327   $214.73   $214.75   $214.70  
  Purchase #5 $132.54   3.332%   $136.9562   $136.96   $136.95   $137.00  
  Purchase #6 $36.82   5.817%   $38.9618   $38.96   $38.95   $39.00  
  Purchase #7 $134.88   9.447%   $147.6221   $147.62   $147.60   $147.60  
  7 purchase totals = $988.35       $1,069.1855   $1,069.18   $1,069.15   $1,069.20