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 $96.33   8.307%   $104.3321   $104.33   $104.35   $104.30  
  Purchase #2 $166.59   10.272%   $183.7021   $183.70   $183.70   $183.70  
  Purchase #3 $220.60   10.639%   $244.0696   $244.07   $244.05   $244.10  
  Purchase #4 $111.99   13.462%   $127.0661   $127.07   $127.05   $127.10  
  Purchase #5 $8.47   7.521%   $9.107   $9.11   $9.10   $9.10  
  Purchase #6 $88.52   12.305%   $99.4124   $99.41   $99.40   $99.40  
  Purchase #7 $17.75   4.657%   $18.5766   $18.58   $18.60   $18.60  
  7 purchase totals = $710.25       $786.2659   $786.27   $786.25   $786.30