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 $88.48   4.446%   $92.4138   $92.41   $92.40   $92.40  
  Purchase #2 $154.99   11.607%   $172.9797   $172.98   $173.00   $173.00  
  Purchase #3 $216.96   13.795%   $246.8896   $246.89   $246.90   $246.90  
  Purchase #4 $92.86   10.577%   $102.6818   $102.68   $102.70   $102.70  
  Purchase #5 $188.46   12.538%   $212.0891   $212.09   $212.10   $212.10  
  Purchase #6 $153.76   9.834%   $168.8808   $168.88   $168.90   $168.90  
  Purchase #7 $81.54   12.815%   $91.9894   $91.99   $92.00   $92.00  
  7 purchase totals = $977.05       $1,087.9242   $1,087.92   $1,088.00   $1,088.00