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 $24.68   8.119%   $26.6838   $26.68   $26.70   $26.70  
  Purchase #2 $192.90   9.366%   $210.967   $210.97   $210.95   $211.00  
  Purchase #3 $225.61   9.452%   $246.9347   $246.93   $246.95   $246.90  
  Purchase #4 $212.76   12.250%   $238.8231   $238.82   $238.80   $238.80  
  Purchase #5 $228.55   8.438%   $247.835   $247.84   $247.85   $247.80  
  Purchase #6 $35.78   6.196%   $37.9969   $38.00   $38.00   $38.00  
  Purchase #7 $192.57   12.758%   $217.1381   $217.14   $217.15   $217.10  
  7 purchase totals = $1,112.85       $1,226.3786   $1,226.38   $1,226.40   $1,226.30