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 $200.32   11.322%   $223.0002   $223.00   $223.00   $223.00  
  Purchase #2 $244.44   6.377%   $260.0279   $260.03   $260.05   $260.00  
  Purchase #3 $239.99   7.164%   $257.1829   $257.18   $257.20   $257.20  
  Purchase #4 $147.77   10.659%   $163.5208   $163.52   $163.50   $163.50  
  Purchase #5 $10.55   3.863%   $10.9575   $10.96   $10.95   $11.00  
  Purchase #6 $14.38   6.534%   $15.3196   $15.32   $15.30   $15.30  
  Purchase #7 $60.29   10.444%   $66.5867   $66.59   $66.60   $66.60  
  7 purchase totals = $917.74       $996.5956   $996.60   $996.60   $996.60