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 $152.94   13.104%   $172.9813   $172.98   $173.00   $173.00  
  Purchase #2 $17.67   5.186%   $18.5864   $18.59   $18.60   $18.60  
  Purchase #3 $179.26   7.664%   $192.9985   $193.00   $193.00   $193.00  
  Purchase #4 $233.68   11.439%   $260.4107   $260.41   $260.40   $260.40  
  Purchase #5 $199.55   7.397%   $214.3107   $214.31   $214.30   $214.30  
  Purchase #6 $197.92   6.336%   $210.4602   $210.46   $210.45   $210.50  
  Purchase #7 $80.97   9.676%   $88.8047   $88.80   $88.80   $88.80  
  7 purchase totals = $1,061.99       $1,158.5525   $1,158.55   $1,158.55   $1,158.60