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 $10.33   13.699%   $11.7451   $11.75   $11.75   $11.70  
  Purchase #2 $211.54   4.565%   $221.1968   $221.20   $221.20   $221.20  
  Purchase #3 $8.31   11.184%   $9.2394   $9.24   $9.25   $9.20  
  Purchase #4 $204.30   5.526%   $215.5896   $215.59   $215.60   $215.60  
  Purchase #5 $219.99   13.620%   $249.9526   $249.95   $249.95   $250.00  
  Purchase #6 $101.92   4.199%   $106.1996   $106.20   $106.20   $106.20  
  Purchase #7 $168.29   3.836%   $174.7456   $174.75   $174.75   $174.70  
  7 purchase totals = $924.68       $988.6687   $988.68   $988.70   $988.60