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 $101.83   6.620%   $108.5711   $108.57   $108.55   $108.60  
  Purchase #2 $98.38   4.326%   $102.6359   $102.64   $102.65   $102.60  
  Purchase #3 $22.96   13.104%   $25.9687   $25.97   $25.95   $26.00  
  Purchase #4 $60.32   13.621%   $68.5362   $68.54   $68.55   $68.50  
  Purchase #5 $9.88   10.597%   $10.927   $10.93   $10.95   $10.90  
  Purchase #6 $41.54   8.791%   $45.1918   $45.19   $45.20   $45.20  
  Purchase #7 $223.91   7.322%   $240.3047   $240.30   $240.30   $240.30  
  7 purchase totals = $558.82       $602.1354   $602.14   $602.15   $602.10