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 $183.64   11.611%   $204.9624   $204.96   $204.95   $205.00  
  Purchase #2 $147.57   10.816%   $163.5312   $163.53   $163.55   $163.50  
  Purchase #3 $55.87   10.772%   $61.8883   $61.89   $61.90   $61.90  
  Purchase #4 $28.30   11.735%   $31.621   $31.62   $31.60   $31.60  
  Purchase #5 $134.98   12.799%   $152.2561   $152.26   $152.25   $152.30  
  Purchase #6 $205.68   6.126%   $218.28   $218.28   $218.30   $218.30  
  Purchase #7 $243.46   7.670%   $262.1334   $262.13   $262.15   $262.10  
  7 purchase totals = $999.50       $1,094.6724   $1,094.67   $1,094.70   $1,094.70