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 $24.40   7.629%   $26.2615   $26.26   $26.25   $26.30  
  Purchase #2 $122.69   8.260%   $132.8242   $132.82   $132.80   $132.80  
  Purchase #3 $156.44   4.727%   $163.8349   $163.83   $163.85   $163.80  
  Purchase #4 $125.36   7.236%   $134.431   $134.43   $134.45   $134.40  
  Purchase #5 $165.53   8.212%   $179.1233   $179.12   $179.10   $179.10  
  Purchase #6 $135.50   6.331%   $144.0785   $144.08   $144.10   $144.10  
  Purchase #7 $32.92   9.424%   $36.0224   $36.02   $36.00   $36.00  
  7 purchase totals = $762.84       $816.5758   $816.56   $816.55   $816.50