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 $64.75   4.281%   $67.5219   $67.52   $67.50   $67.50  
  Purchase #2 $193.76   10.539%   $214.1804   $214.18   $214.20   $214.20  
  Purchase #3 $198.33   11.399%   $220.9376   $220.94   $220.95   $220.90  
  Purchase #4 $220.25   9.821%   $241.8808   $241.88   $241.90   $241.90  
  Purchase #5 $174.59   10.475%   $192.8783   $192.88   $192.90   $192.90  
  Purchase #6 $111.56   11.558%   $124.4541   $124.45   $124.45   $124.50  
  Purchase #7 $194.76   5.675%   $205.8126   $205.81   $205.80   $205.80  
  7 purchase totals = $1,158.00       $1,267.6657   $1,267.66   $1,267.70   $1,267.70