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 $81.43   6.803%   $86.9697   $86.97   $86.95   $87.00  
  Purchase #2 $218.37   9.234%   $238.5343   $238.53   $238.55   $238.50  
  Purchase #3 $113.34   10.112%   $124.8009   $124.80   $124.80   $124.80  
  Purchase #4 $60.92   3.213%   $62.8774   $62.88   $62.90   $62.90  
  Purchase #5 $150.61   12.198%   $168.9814   $168.98   $169.00   $169.00  
  Purchase #6 $73.87   10.850%   $81.8849   $81.88   $81.90   $81.90  
  Purchase #7 $10.72   10.544%   $11.8503   $11.85   $11.85   $11.90  
  7 purchase totals = $709.26       $775.8989   $775.89   $775.95   $776.00