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 $86.44   11.118%   $96.0504   $96.05   $96.05   $96.10  
  Purchase #2 $178.65   9.829%   $196.2095   $196.21   $196.20   $196.20  
  Purchase #3 $79.45   12.796%   $89.6164   $89.62   $89.60   $89.60  
  Purchase #4 $24.83   7.526%   $26.6987   $26.70   $26.70   $26.70  
  Purchase #5 $222.55   7.242%   $238.6671   $238.67   $238.65   $238.70  
  Purchase #6 $187.64   5.449%   $197.8645   $197.86   $197.85   $197.90  
  Purchase #7 $45.47   9.378%   $49.7342   $49.73   $49.75   $49.70  
  7 purchase totals = $825.03       $894.8408   $894.84   $894.80   $894.90