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 $24.51   6.742%   $26.1625   $26.16   $26.15   $26.20  
  Purchase #2 $112.43   10.229%   $123.9305   $123.93   $123.95   $123.90  
  Purchase #3 $177.35   11.364%   $197.5041   $197.50   $197.50   $197.50  
  Purchase #4 $154.56   12.594%   $174.0253   $174.03   $174.05   $174.00  
  Purchase #5 $88.62   11.801%   $99.078   $99.08   $99.10   $99.10  
  Purchase #6 $163.60   8.218%   $177.0446   $177.04   $177.05   $177.00  
  Purchase #7 $199.61   10.521%   $220.611   $220.61   $220.60   $220.60  
  7 purchase totals = $920.68       $1,018.3560   $1,018.35   $1,018.40   $1,018.30