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 $172.72   12.292%   $193.9507   $193.95   $193.95   $194.00  
  Purchase #2 $229.64   7.413%   $246.6632   $246.66   $246.65   $246.70  
  Purchase #3 $200.36   4.169%   $208.713   $208.71   $208.70   $208.70  
  Purchase #4 $175.88   6.567%   $187.43   $187.43   $187.45   $187.40  
  Purchase #5 $92.75   5.194%   $97.5674   $97.57   $97.55   $97.60  
  Purchase #6 $151.42   8.451%   $164.2165   $164.22   $164.20   $164.20  
  Purchase #7 $165.36   12.679%   $186.326   $186.33   $186.35   $186.30  
  7 purchase totals = $1,188.13       $1,284.8668   $1,284.87   $1,284.85   $1,284.90