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 $249.33   5.746%   $263.6565   $263.66   $263.65   $263.70  
  Purchase #2 $64.79   12.689%   $73.0112   $73.01   $73.00   $73.00  
  Purchase #3 $238.66   3.471%   $246.9439   $246.94   $246.95   $246.90  
  Purchase #4 $125.64   9.486%   $137.5582   $137.56   $137.55   $137.60  
  Purchase #5 $77.41   8.114%   $83.691   $83.69   $83.70   $83.70  
  Purchase #6 $167.26   11.217%   $186.0216   $186.02   $186.00   $186.00  
  Purchase #7 $60.85   6.237%   $64.6452   $64.65   $64.65   $64.60  
  7 purchase totals = $983.94       $1,055.5276   $1,055.53   $1,055.50   $1,055.50