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 $31.31   5.187%   $32.934   $32.93   $32.95   $32.90  
  Purchase #2 $242.51   11.247%   $269.7851   $269.79   $269.80   $269.80  
  Purchase #3 $220.70   4.236%   $230.0489   $230.05   $230.05   $230.00  
  Purchase #4 $56.28   10.144%   $61.989   $61.99   $62.00   $62.00  
  Purchase #5 $71.61   10.663%   $79.2458   $79.25   $79.25   $79.20  
  Purchase #6 $245.25   5.178%   $257.949   $257.95   $257.95   $257.90  
  Purchase #7 $79.99   11.681%   $89.3336   $89.33   $89.35   $89.30  
  7 purchase totals = $947.65       $1,021.2854   $1,021.29   $1,021.35   $1,021.10