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 $84.65   13.324%   $95.9288   $95.93   $95.95   $95.90  
  Purchase #2 $106.31   8.363%   $115.2007   $115.20   $115.20   $115.20  
  Purchase #3 $232.35   8.794%   $252.7829   $252.78   $252.80   $252.80  
  Purchase #4 $55.93   12.287%   $62.8021   $62.80   $62.80   $62.80  
  Purchase #5 $99.30   10.264%   $109.4922   $109.49   $109.50   $109.50  
  Purchase #6 $190.89   5.660%   $201.6944   $201.69   $201.70   $201.70  
  Purchase #7 $37.84   5.708%   $39.9999   $40.00   $40.00   $40.00  
  7 purchase totals = $807.27       $877.9010   $877.89   $877.95   $877.90