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 $162.51   13.785%   $184.912   $184.91   $184.90   $184.90  
  Purchase #2 $68.42   8.374%   $74.1495   $74.15   $74.15   $74.10  
  Purchase #3 $64.29   3.372%   $66.4579   $66.46   $66.45   $66.50  
  Purchase #4 $230.33   6.148%   $244.4907   $244.49   $244.50   $244.50  
  Purchase #5 $238.37   12.489%   $268.14   $268.14   $268.15   $268.10  
  Purchase #6 $15.87   8.757%   $17.2597   $17.26   $17.25   $17.30  
  Purchase #7 $245.57   3.685%   $254.6193   $254.62   $254.60   $254.60  
  7 purchase totals = $1,025.36       $1,110.0291   $1,110.03   $1,110.00   $1,110.00