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 $60.86   10.572%   $67.2941   $67.29   $67.30   $67.30  
  Purchase #2 $155.41   10.630%   $171.9301   $171.93   $171.95   $171.90  
  Purchase #3 $114.26   11.264%   $127.1302   $127.13   $127.15   $127.10  
  Purchase #4 $177.94   9.780%   $195.3425   $195.34   $195.35   $195.30  
  Purchase #5 $216.68   5.394%   $228.3677   $228.37   $228.35   $228.40  
  Purchase #6 $117.85   6.191%   $125.1461   $125.15   $125.15   $125.10  
  Purchase #7 $98.65   10.703%   $109.2085   $109.21   $109.20   $109.20  
  7 purchase totals = $941.65       $1,024.4192   $1,024.42   $1,024.45   $1,024.30