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 $204.63   13.722%   $232.7093   $232.71   $232.70   $232.70  
  Purchase #2 $115.86   6.613%   $123.5218   $123.52   $123.50   $123.50  
  Purchase #3 $203.77   10.395%   $224.9519   $224.95   $224.95   $225.00  
  Purchase #4 $117.41   13.572%   $133.3449   $133.34   $133.35   $133.30  
  Purchase #5 $216.32   7.520%   $232.5873   $232.59   $232.60   $232.60  
  Purchase #6 $55.80   5.265%   $58.7379   $58.74   $58.75   $58.70  
  Purchase #7 $57.90   10.727%   $64.1109   $64.11   $64.10   $64.10  
  7 purchase totals = $971.69       $1,069.9640   $1,069.96   $1,069.95   $1,069.90