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 $194.95   12.815%   $219.9328   $219.93   $219.95   $219.90  
  Purchase #2 $68.25   9.825%   $74.9556   $74.96   $74.95   $75.00  
  Purchase #3 $150.88   3.555%   $156.2438   $156.24   $156.25   $156.20  
  Purchase #4 $55.68   5.186%   $58.5676   $58.57   $58.55   $58.60  
  Purchase #5 $191.50   6.260%   $203.4879   $203.49   $203.50   $203.50  
  Purchase #6 $246.63   11.373%   $274.6792   $274.68   $274.70   $274.70  
  Purchase #7 $11.92   8.249%   $12.9033   $12.90   $12.90   $12.90  
  7 purchase totals = $919.81       $1,000.7702   $1,000.77   $1,000.80   $1,000.80