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 $242.57   8.813%   $263.9477   $263.95   $263.95   $263.90  
  Purchase #2 $192.54   3.270%   $198.8361   $198.84   $198.85   $198.80  
  Purchase #3 $54.98   13.218%   $62.2473   $62.25   $62.25   $62.20  
  Purchase #4 $228.64   5.251%   $240.6459   $240.65   $240.65   $240.60  
  Purchase #5 $220.62   10.684%   $244.191   $244.19   $244.20   $244.20  
  Purchase #6 $136.54   11.400%   $152.1056   $152.11   $152.10   $152.10  
  Purchase #7 $121.37   10.721%   $134.3821   $134.38   $134.40   $134.40  
  7 purchase totals = $1,197.26       $1,296.3557   $1,296.37   $1,296.40   $1,296.20