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 $59.51   12.398%   $66.888   $66.89   $66.90   $66.90  
  Purchase #2 $34.81   8.791%   $37.8701   $37.87   $37.85   $37.90  
  Purchase #3 $196.89   8.172%   $212.9799   $212.98   $213.00   $213.00  
  Purchase #4 $81.62   5.322%   $85.9638   $85.96   $85.95   $86.00  
  Purchase #5 $110.98   11.229%   $123.4419   $123.44   $123.45   $123.40  
  Purchase #6 $177.29   13.712%   $201.6   $201.60   $201.60   $201.60  
  Purchase #7 $29.55   3.460%   $30.5724   $30.57   $30.55   $30.60  
  7 purchase totals = $690.65       $759.3161   $759.31   $759.30   $759.40