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 $158.96   11.445%   $177.153   $177.15   $177.15   $177.20  
  Purchase #2 $85.40   12.314%   $95.9162   $95.92   $95.90   $95.90  
  Purchase #3 $233.59   9.397%   $255.5405   $255.54   $255.55   $255.50  
  Purchase #4 $151.56   8.566%   $164.5426   $164.54   $164.55   $164.50  
  Purchase #5 $187.97   13.270%   $212.9136   $212.91   $212.90   $212.90  
  Purchase #6 $181.82   8.756%   $197.7402   $197.74   $197.75   $197.70  
  Purchase #7 $148.36   10.366%   $163.739   $163.74   $163.75   $163.70  
  7 purchase totals = $1,147.66       $1,267.5451   $1,267.54   $1,267.55   $1,267.40