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 $119.86   11.214%   $133.3011   $133.30   $133.30   $133.30  
  Purchase #2 $213.87   8.568%   $232.1944   $232.19   $232.20   $232.20  
  Purchase #3 $200.28   7.453%   $215.2069   $215.21   $215.20   $215.20  
  Purchase #4 $35.60   7.773%   $38.3672   $38.37   $38.35   $38.40  
  Purchase #5 $83.62   12.232%   $93.8484   $93.85   $93.85   $93.80  
  Purchase #6 $237.36   5.827%   $251.191   $251.19   $251.20   $251.20  
  Purchase #7 $186.91   4.107%   $194.5864   $194.59   $194.60   $194.60  
  7 purchase totals = $1,077.50       $1,158.6954   $1,158.70   $1,158.70   $1,158.70