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 $156.91   12.677%   $176.8015   $176.80   $176.80   $176.80  
  Purchase #2 $64.60   3.145%   $66.6317   $66.63   $66.65   $66.60  
  Purchase #3 $142.37   6.180%   $151.1685   $151.17   $151.15   $151.20  
  Purchase #4 $238.98   3.313%   $246.8974   $246.90   $246.90   $246.90  
  Purchase #5 $169.31   6.594%   $180.4743   $180.47   $180.45   $180.50  
  Purchase #6 $47.51   11.126%   $52.796   $52.80   $52.80   $52.80  
  Purchase #7 $162.79   3.394%   $168.3151   $168.32   $168.30   $168.30  
  7 purchase totals = $982.47       $1,043.0845   $1,043.09   $1,043.05   $1,043.10