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 $206.94   11.629%   $231.0051   $231.01   $231.00   $231.00  
  Purchase #2 $109.59   5.788%   $115.9331   $115.93   $115.95   $115.90  
  Purchase #3 $127.60   4.712%   $133.6125   $133.61   $133.60   $133.60  
  Purchase #4 $207.45   3.560%   $214.8352   $214.84   $214.85   $214.80  
  Purchase #5 $70.52   3.799%   $73.1991   $73.20   $73.20   $73.20  
  Purchase #6 $240.36   8.243%   $260.1729   $260.17   $260.15   $260.20  
  Purchase #7 $151.95   8.164%   $164.3552   $164.36   $164.35   $164.40  
  7 purchase totals = $1,114.41       $1,193.1131   $1,193.12   $1,193.10   $1,193.10