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 $46.34   8.396%   $50.2307   $50.23   $50.25   $50.20  
  Purchase #2 $134.98   4.524%   $141.0865   $141.09   $141.10   $141.10  
  Purchase #3 $239.36   11.818%   $267.6476   $267.65   $267.65   $267.60  
  Purchase #4 $220.26   11.415%   $245.4027   $245.40   $245.40   $245.40  
  Purchase #5 $64.50   8.588%   $70.0393   $70.04   $70.05   $70.00  
  Purchase #6 $159.86   12.578%   $179.9672   $179.97   $179.95   $180.00  
  Purchase #7 $124.53   12.569%   $140.1822   $140.18   $140.20   $140.20  
  7 purchase totals = $989.83       $1,094.5562   $1,094.56   $1,094.60   $1,094.50