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 $82.86   12.198%   $92.9673   $92.97   $92.95   $93.00  
  Purchase #2 $157.54   6.729%   $168.1409   $168.14   $168.15   $168.10  
  Purchase #3 $235.32   8.126%   $254.4421   $254.44   $254.45   $254.40  
  Purchase #4 $222.43   7.281%   $238.6251   $238.63   $238.65   $238.60  
  Purchase #5 $166.76   10.535%   $184.3282   $184.33   $184.35   $184.30  
  Purchase #6 $160.28   3.633%   $166.103   $166.10   $166.10   $166.10  
  Purchase #7 $95.29   3.167%   $98.3078   $98.31   $98.30   $98.30  
  7 purchase totals = $1,120.48       $1,202.9144   $1,202.92   $1,202.95   $1,202.80