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 $187.47   10.116%   $206.4345   $206.43   $206.45   $206.40  
  Purchase #2 $227.58   3.672%   $235.9367   $235.94   $235.95   $235.90  
  Purchase #3 $78.31   6.157%   $83.1315   $83.13   $83.15   $83.10  
  Purchase #4 $169.88   12.146%   $190.5136   $190.51   $190.50   $190.50  
  Purchase #5 $203.66   10.330%   $224.6981   $224.70   $224.70   $224.70  
  Purchase #6 $195.49   11.521%   $218.0124   $218.01   $218.00   $218.00  
  Purchase #7 $58.54   3.476%   $60.5749   $60.57   $60.55   $60.60  
  7 purchase totals = $1,120.93       $1,219.3017   $1,219.29   $1,219.30   $1,219.20