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 $92.63   13.570%   $105.1999   $105.20   $105.20   $105.20  
  Purchase #2 $140.49   8.472%   $152.3923   $152.39   $152.40   $152.40  
  Purchase #3 $71.52   7.612%   $76.9641   $76.96   $76.95   $77.00  
  Purchase #4 $208.65   7.360%   $224.0066   $224.01   $224.00   $224.00  
  Purchase #5 $173.32   10.496%   $191.5117   $191.51   $191.50   $191.50  
  Purchase #6 $9.93   6.438%   $10.5693   $10.57   $10.55   $10.60  
  Purchase #7 $217.60   11.856%   $243.3987   $243.40   $243.40   $243.40  
  7 purchase totals = $914.14       $1,004.0426   $1,004.04   $1,004.00   $1,004.10