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 $87.56   7.393%   $94.0333   $94.03   $94.05   $94.00  
  Purchase #2 $70.98   5.222%   $74.6866   $74.69   $74.70   $74.70  
  Purchase #3 $181.54   10.583%   $200.7524   $200.75   $200.75   $200.80  
  Purchase #4 $247.64   10.260%   $273.0479   $273.05   $273.05   $273.00  
  Purchase #5 $157.27   4.254%   $163.9603   $163.96   $163.95   $164.00  
  Purchase #6 $97.97   10.870%   $108.6193   $108.62   $108.60   $108.60  
  Purchase #7 $127.75   9.663%   $140.0945   $140.09   $140.10   $140.10  
  7 purchase totals = $970.71       $1,055.1943   $1,055.19   $1,055.20   $1,055.20