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 $163.76   13.553%   $185.9544   $185.95   $185.95   $186.00  
  Purchase #2 $112.27   7.468%   $120.6543   $120.65   $120.65   $120.70  
  Purchase #3 $199.64   3.429%   $206.4857   $206.49   $206.50   $206.50  
  Purchase #4 $219.93   4.546%   $229.928   $229.93   $229.95   $229.90  
  Purchase #5 $244.76   8.415%   $265.3566   $265.36   $265.35   $265.40  
  Purchase #6 $222.98   5.541%   $235.3353   $235.34   $235.35   $235.30  
  Purchase #7 $131.71   11.738%   $147.1701   $147.17   $147.15   $147.20  
  7 purchase totals = $1,295.05       $1,390.8844   $1,390.89   $1,390.90   $1,391.00