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 $122.25   3.821%   $126.9212   $126.92   $126.90   $126.90  
  Purchase #2 $164.31   11.658%   $183.4653   $183.47   $183.45   $183.50  
  Purchase #3 $187.99   6.522%   $200.2507   $200.25   $200.25   $200.30  
  Purchase #4 $62.36   8.295%   $67.5328   $67.53   $67.55   $67.50  
  Purchase #5 $204.86   6.870%   $218.9339   $218.93   $218.95   $218.90  
  Purchase #6 $246.72   10.644%   $272.9809   $272.98   $273.00   $273.00  
  Purchase #7 $62.93   7.320%   $67.5365   $67.54   $67.55   $67.50  
  7 purchase totals = $1,051.42       $1,137.6213   $1,137.62   $1,137.65   $1,137.60