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 $35.25   9.551%   $38.6167   $38.62   $38.60   $38.60  
  Purchase #2 $81.72   12.188%   $91.68   $91.68   $91.70   $91.70  
  Purchase #3 $176.68   5.479%   $186.3603   $186.36   $186.35   $186.40  
  Purchase #4 $204.71   6.771%   $218.5709   $218.57   $218.55   $218.60  
  Purchase #5 $142.90   4.109%   $148.7718   $148.77   $148.75   $148.80  
  Purchase #6 $131.50   3.438%   $136.021   $136.02   $136.00   $136.00  
  Purchase #7 $212.44   13.756%   $241.6632   $241.66   $241.65   $241.70  
  7 purchase totals = $985.20       $1,061.6839   $1,061.68   $1,061.60   $1,061.80