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 $199.28   7.811%   $214.8458   $214.85   $214.85   $214.80  
  Purchase #2 $217.55   13.378%   $246.6538   $246.65   $246.65   $246.70  
  Purchase #3 $14.64   6.454%   $15.5849   $15.58   $15.60   $15.60  
  Purchase #4 $119.54   8.266%   $129.4212   $129.42   $129.40   $129.40  
  Purchase #5 $76.68   12.144%   $85.992   $85.99   $86.00   $86.00  
  Purchase #6 $160.34   12.651%   $180.6246   $180.62   $180.60   $180.60  
  Purchase #7 $169.32   8.459%   $183.6428   $183.64   $183.65   $183.60  
  7 purchase totals = $957.35       $1,056.7651   $1,056.75   $1,056.75   $1,056.70