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 $88.68   7.851%   $95.6423   $95.64   $95.65   $95.60  
  Purchase #2 $66.36   6.482%   $70.6615   $70.66   $70.65   $70.70  
  Purchase #3 $227.85   9.707%   $249.9674   $249.97   $249.95   $250.00  
  Purchase #4 $192.94   9.857%   $211.9581   $211.96   $211.95   $212.00  
  Purchase #5 $213.75   12.726%   $240.9518   $240.95   $240.95   $241.00  
  Purchase #6 $56.50   6.463%   $60.1516   $60.15   $60.15   $60.20  
  Purchase #7 $71.48   7.864%   $77.1012   $77.10   $77.10   $77.10  
  7 purchase totals = $917.56       $1,006.4339   $1,006.43   $1,006.40   $1,006.60