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 $146.46   7.716%   $157.7609   $157.76   $157.75   $157.80  
  Purchase #2 $82.74   11.596%   $92.3345   $92.33   $92.35   $92.30  
  Purchase #3 $154.63   13.272%   $175.1525   $175.15   $175.15   $175.20  
  Purchase #4 $124.65   3.666%   $129.2197   $129.22   $129.20   $129.20  
  Purchase #5 $50.81   4.457%   $53.0746   $53.07   $53.05   $53.10  
  Purchase #6 $188.38   8.820%   $204.9951   $205.00   $205.00   $205.00  
  Purchase #7 $190.41   12.368%   $213.9599   $213.96   $213.95   $214.00  
  7 purchase totals = $938.08       $1,026.4972   $1,026.49   $1,026.45   $1,026.60