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 $168.46   11.570%   $187.9508   $187.95   $187.95   $188.00  
  Purchase #2 $30.86   8.592%   $33.5115   $33.51   $33.50   $33.50  
  Purchase #3 $135.62   8.124%   $146.6378   $146.64   $146.65   $146.60  
  Purchase #4 $147.32   4.507%   $153.9597   $153.96   $153.95   $154.00  
  Purchase #5 $203.87   13.761%   $231.9246   $231.92   $231.90   $231.90  
  Purchase #6 $171.46   3.562%   $177.5674   $177.57   $177.55   $177.60  
  Purchase #7 $145.87   4.285%   $152.1205   $152.12   $152.10   $152.10  
  7 purchase totals = $1,003.46       $1,083.6723   $1,083.67   $1,083.60   $1,083.70