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 $134.83   11.611%   $150.4851   $150.49   $150.50   $150.50  
  Purchase #2 $15.46   7.413%   $16.606   $16.61   $16.60   $16.60  
  Purchase #3 $138.48   3.435%   $143.2368   $143.24   $143.25   $143.20  
  Purchase #4 $56.88   5.406%   $59.9549   $59.95   $59.95   $60.00  
  Purchase #5 $50.95   10.552%   $56.3262   $56.33   $56.35   $56.30  
  Purchase #6 $239.83   9.561%   $262.7601   $262.76   $262.75   $262.80  
  Purchase #7 $155.84   10.115%   $171.6032   $171.60   $171.60   $171.60  
  7 purchase totals = $792.27       $860.9723   $860.98   $861.00   $861.00