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 $87.30   9.498%   $95.5918   $95.59   $95.60   $95.60  
  Purchase #2 $147.33   8.142%   $159.3256   $159.33   $159.35   $159.30  
  Purchase #3 $101.27   5.163%   $106.4986   $106.50   $106.50   $106.50  
  Purchase #4 $197.48   3.855%   $205.0929   $205.09   $205.10   $205.10  
  Purchase #5 $131.94   13.240%   $149.4089   $149.41   $149.40   $149.40  
  Purchase #6 $67.40   13.715%   $76.6439   $76.64   $76.65   $76.60  
  Purchase #7 $221.94   5.781%   $234.7704   $234.77   $234.75   $234.80  
  7 purchase totals = $954.66       $1,027.3321   $1,027.33   $1,027.35   $1,027.30