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 $206.47   7.501%   $221.9573   $221.96   $221.95   $222.00  
  Purchase #2 $184.90   6.826%   $197.5213   $197.52   $197.50   $197.50  
  Purchase #3 $136.66   7.401%   $146.7742   $146.77   $146.75   $146.80  
  Purchase #4 $181.88   9.370%   $198.9222   $198.92   $198.90   $198.90  
  Purchase #5 $162.43   6.542%   $173.0562   $173.06   $173.05   $173.10  
  Purchase #6 $217.70   12.378%   $244.6469   $244.65   $244.65   $244.60  
  Purchase #7 $178.48   5.767%   $188.7729   $188.77   $188.75   $188.80  
  7 purchase totals = $1,268.52       $1,371.6510   $1,371.65   $1,371.55   $1,371.70