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 $250.87   12.643%   $282.5875   $282.59   $282.60   $282.60  
  Purchase #2 $189.53   6.831%   $202.4768   $202.48   $202.50   $202.50  
  Purchase #3 $215.82   3.743%   $223.8981   $223.90   $223.90   $223.90  
  Purchase #4 $244.58   13.615%   $277.8796   $277.88   $277.90   $277.90  
  Purchase #5 $181.80   6.450%   $193.5261   $193.53   $193.55   $193.50  
  Purchase #6 $53.96   10.808%   $59.792   $59.79   $59.80   $59.80  
  Purchase #7 $210.44   7.310%   $225.8232   $225.82   $225.80   $225.80  
  7 purchase totals = $1,347.00       $1,465.9833   $1,465.99   $1,466.05   $1,466.00