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 $32.82   13.836%   $37.361   $37.36   $37.35   $37.40  
  Purchase #2 $138.61   10.759%   $153.523   $153.52   $153.50   $153.50  
  Purchase #3 $125.40   5.728%   $132.5829   $132.58   $132.60   $132.60  
  Purchase #4 $78.48   9.612%   $86.0235   $86.02   $86.00   $86.00  
  Purchase #5 $181.66   7.326%   $194.9684   $194.97   $194.95   $195.00  
  Purchase #6 $145.62   8.407%   $157.8623   $157.86   $157.85   $157.90  
  Purchase #7 $194.76   10.157%   $214.5418   $214.54   $214.55   $214.50  
  7 purchase totals = $897.35       $976.8629   $976.85   $976.80   $976.90