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 $66.83   6.573%   $71.2227   $71.22   $71.20   $71.20  
  Purchase #2 $182.93   13.165%   $207.0127   $207.01   $207.00   $207.00  
  Purchase #3 $22.87   13.763%   $26.0176   $26.02   $26.00   $26.00  
  Purchase #4 $158.60   5.338%   $167.0661   $167.07   $167.05   $167.10  
  Purchase #5 $132.65   4.382%   $138.4627   $138.46   $138.45   $138.50  
  Purchase #6 $197.35   10.477%   $218.0264   $218.03   $218.05   $218.00  
  Purchase #7 $182.36   9.586%   $199.841   $199.84   $199.85   $199.80  
  7 purchase totals = $943.59       $1,027.6492   $1,027.65   $1,027.60   $1,027.60