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 $48.84   4.867%   $51.217   $51.22   $51.20   $51.20  
  Purchase #2 $181.91   8.232%   $196.8848   $196.88   $196.90   $196.90  
  Purchase #3 $6.58   6.109%   $6.982   $6.98   $7.00   $7.00  
  Purchase #4 $247.77   5.781%   $262.0936   $262.09   $262.10   $262.10  
  Purchase #5 $8.43   11.266%   $9.3797   $9.38   $9.40   $9.40  
  Purchase #6 $203.69   11.545%   $227.206   $227.21   $227.20   $227.20  
  Purchase #7 $128.79   10.109%   $141.8094   $141.81   $141.80   $141.80  
  7 purchase totals = $826.01       $895.5725   $895.57   $895.60   $895.60