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 $87.95   6.401%   $93.5797   $93.58   $93.60   $93.60  
  Purchase #2 $59.58   8.588%   $64.6967   $64.70   $64.70   $64.70  
  Purchase #3 $239.53   3.833%   $248.7112   $248.71   $248.70   $248.70  
  Purchase #4 $182.67   4.607%   $191.0856   $191.09   $191.10   $191.10  
  Purchase #5 $158.56   3.835%   $164.6408   $164.64   $164.65   $164.60  
  Purchase #6 $56.57   9.818%   $62.124   $62.12   $62.10   $62.10  
  Purchase #7 $174.40   3.591%   $180.6627   $180.66   $180.65   $180.70  
  7 purchase totals = $959.26       $1,005.5007   $1,005.50   $1,005.50   $1,005.50