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 $88.65   8.479%   $96.1666   $96.17   $96.15   $96.20  
  Purchase #2 $225.64   12.408%   $253.6374   $253.64   $253.65   $253.60  
  Purchase #3 $178.34   12.129%   $199.9709   $199.97   $199.95   $200.00  
  Purchase #4 $85.65   3.637%   $88.7651   $88.77   $88.75   $88.80  
  Purchase #5 $85.39   4.851%   $89.5323   $89.53   $89.55   $89.50  
  Purchase #6 $80.51   7.809%   $86.797   $86.80   $86.80   $86.80  
  Purchase #7 $122.32   10.242%   $134.848   $134.85   $134.85   $134.80  
  7 purchase totals = $866.50       $949.7173   $949.73   $949.70   $949.70