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 $88.76   3.492%   $91.8595   $91.86   $91.85   $91.90  
  Purchase #2 $69.81   4.629%   $73.0415   $73.04   $73.05   $73.00  
  Purchase #3 $5.44   10.579%   $6.0155   $6.02   $6.00   $6.00  
  Purchase #4 $184.39   10.357%   $203.4873   $203.49   $203.50   $203.50  
  Purchase #5 $95.89   11.493%   $106.9106   $106.91   $106.90   $106.90  
  Purchase #6 $227.84   5.758%   $240.959   $240.96   $240.95   $241.00  
  Purchase #7 $128.50   3.187%   $132.5953   $132.60   $132.60   $132.60  
  7 purchase totals = $800.63       $854.8687   $854.88   $854.85   $854.90