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 $115.46   9.765%   $126.7347   $126.73   $126.75   $126.70  
  Purchase #2 $186.74   9.595%   $204.6577   $204.66   $204.65   $204.70  
  Purchase #3 $183.49   7.498%   $197.2481   $197.25   $197.25   $197.20  
  Purchase #4 $162.45   6.439%   $172.9102   $172.91   $172.90   $172.90  
  Purchase #5 $207.60   9.186%   $226.6701   $226.67   $226.65   $226.70  
  Purchase #6 $131.67   5.338%   $138.6985   $138.70   $138.70   $138.70  
  Purchase #7 $231.87   12.361%   $260.5315   $260.53   $260.55   $260.50  
  7 purchase totals = $1,219.28       $1,327.4508   $1,327.45   $1,327.45   $1,327.40