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 $131.53   8.830%   $143.1441   $143.14   $143.15   $143.10  
  Purchase #2 $193.51   4.331%   $201.8909   $201.89   $201.90   $201.90  
  Purchase #3 $59.56   8.484%   $64.6131   $64.61   $64.60   $64.60  
  Purchase #4 $172.42   11.843%   $192.8397   $192.84   $192.85   $192.80  
  Purchase #5 $98.60   8.291%   $106.7749   $106.77   $106.75   $106.80  
  Purchase #6 $205.78   9.520%   $225.3703   $225.37   $225.35   $225.40  
  Purchase #7 $13.56   10.395%   $14.9696   $14.97   $14.95   $15.00  
  7 purchase totals = $874.96       $949.6026   $949.59   $949.55   $949.60