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 $234.43   11.178%   $260.6346   $260.63   $260.65   $260.60  
  Purchase #2 $30.47   4.447%   $31.825   $31.83   $31.85   $31.80  
  Purchase #3 $84.37   12.608%   $95.0074   $95.01   $95.00   $95.00  
  Purchase #4 $62.40   5.855%   $66.0535   $66.05   $66.05   $66.10  
  Purchase #5 $71.73   4.173%   $74.7233   $74.72   $74.70   $74.70  
  Purchase #6 $209.65   11.526%   $233.8143   $233.81   $233.80   $233.80  
  Purchase #7 $93.65   13.721%   $106.4997   $106.50   $106.50   $106.50  
  7 purchase totals = $786.70       $868.5578   $868.55   $868.55   $868.50