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 $56.92   13.573%   $64.6458   $64.65   $64.65   $64.60  
  Purchase #2 $191.40   5.334%   $201.6093   $201.61   $201.60   $201.60  
  Purchase #3 $159.40   13.727%   $181.2808   $181.28   $181.30   $181.30  
  Purchase #4 $147.26   11.139%   $163.6633   $163.66   $163.65   $163.70  
  Purchase #5 $73.56   4.502%   $76.8717   $76.87   $76.85   $76.90  
  Purchase #6 $181.90   4.828%   $190.6821   $190.68   $190.70   $190.70  
  Purchase #7 $162.25   3.571%   $168.0439   $168.04   $168.05   $168.00  
  7 purchase totals = $972.69       $1,046.7969   $1,046.79   $1,046.80   $1,046.80