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 $243.43   10.199%   $268.2574   $268.26   $268.25   $268.30  
  Purchase #2 $127.41   5.837%   $134.8469   $134.85   $134.85   $134.80  
  Purchase #3 $57.85   5.253%   $60.8889   $60.89   $60.90   $60.90  
  Purchase #4 $119.37   9.744%   $131.0014   $131.00   $131.00   $131.00  
  Purchase #5 $88.29   3.809%   $91.653   $91.65   $91.65   $91.70  
  Purchase #6 $212.60   5.473%   $224.2356   $224.24   $224.25   $224.20  
  Purchase #7 $127.49   13.193%   $144.3098   $144.31   $144.30   $144.30  
  7 purchase totals = $976.44       $1,055.1930   $1,055.20   $1,055.20   $1,055.20