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 $24.32   10.592%   $26.896   $26.90   $26.90   $26.90  
  Purchase #2 $204.85   13.243%   $231.9783   $231.98   $232.00   $232.00  
  Purchase #3 $48.59   6.565%   $51.7799   $51.78   $51.80   $51.80  
  Purchase #4 $69.31   9.157%   $75.6567   $75.66   $75.65   $75.70  
  Purchase #5 $94.88   11.636%   $105.9202   $105.92   $105.90   $105.90  
  Purchase #6 $119.33   5.664%   $126.0889   $126.09   $126.10   $126.10  
  Purchase #7 $230.61   3.511%   $238.7067   $238.71   $238.70   $238.70  
  7 purchase totals = $791.89       $857.0267   $857.04   $857.05   $857.10