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 $105.52   13.524%   $119.7905   $119.79   $119.80   $119.80  
  Purchase #2 $233.30   13.115%   $263.8973   $263.90   $263.90   $263.90  
  Purchase #3 $157.99   9.415%   $172.8648   $172.86   $172.85   $172.90  
  Purchase #4 $247.80   4.797%   $259.687   $259.69   $259.70   $259.70  
  Purchase #5 $62.78   11.199%   $69.8107   $69.81   $69.80   $69.80  
  Purchase #6 $186.82   8.537%   $202.7688   $202.77   $202.75   $202.80  
  Purchase #7 $187.55   5.415%   $197.7058   $197.71   $197.70   $197.70  
  7 purchase totals = $1,181.76       $1,286.5249   $1,286.53   $1,286.50   $1,286.60