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 $24.73   8.148%   $26.745   $26.75   $26.75   $26.70  
  Purchase #2 $83.83   10.543%   $92.6682   $92.67   $92.65   $92.70  
  Purchase #3 $84.31   6.506%   $89.7952   $89.80   $89.80   $89.80  
  Purchase #4 $205.26   5.619%   $216.7936   $216.79   $216.80   $216.80  
  Purchase #5 $29.91   12.272%   $33.5806   $33.58   $33.60   $33.60  
  Purchase #6 $145.77   10.859%   $161.5992   $161.60   $161.60   $161.60  
  Purchase #7 $70.74   8.664%   $76.8689   $76.87   $76.85   $76.90  
  7 purchase totals = $644.55       $698.0507   $698.06   $698.05   $698.10