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 $147.26   13.763%   $167.5274   $167.53   $167.55   $167.50  
  Purchase #2 $202.64   5.751%   $214.2938   $214.29   $214.30   $214.30  
  Purchase #3 $134.25   4.129%   $139.7932   $139.79   $139.80   $139.80  
  Purchase #4 $71.53   13.590%   $81.2509   $81.25   $81.25   $81.30  
  Purchase #5 $151.29   8.295%   $163.8395   $163.84   $163.85   $163.80  
  Purchase #6 $191.32   12.140%   $214.5462   $214.55   $214.55   $214.50  
  Purchase #7 $29.36   3.113%   $30.274   $30.27   $30.25   $30.30  
  7 purchase totals = $927.65       $1,011.5250   $1,011.52   $1,011.55   $1,011.50