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 $201.79   12.824%   $227.6675   $227.67   $227.65   $227.70  
  Purchase #2 $145.47   10.692%   $161.0237   $161.02   $161.00   $161.00  
  Purchase #3 $250.60   6.448%   $266.7587   $266.76   $266.75   $266.80  
  Purchase #4 $67.47   6.230%   $71.6734   $71.67   $71.65   $71.70  
  Purchase #5 $200.35   7.755%   $215.8871   $215.89   $215.90   $215.90  
  Purchase #6 $211.61   9.690%   $232.115   $232.12   $232.10   $232.10  
  Purchase #7 $30.81   8.606%   $33.4615   $33.46   $33.45   $33.50  
  7 purchase totals = $1,108.10       $1,208.5869   $1,208.59   $1,208.50   $1,208.70