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 $83.64   10.706%   $92.5945   $92.59   $92.60   $92.60  
  Purchase #2 $122.49   7.212%   $131.324   $131.32   $131.30   $131.30  
  Purchase #3 $103.99   10.327%   $114.729   $114.73   $114.75   $114.70  
  Purchase #4 $243.48   13.581%   $276.547   $276.55   $276.55   $276.50  
  Purchase #5 $70.59   7.203%   $75.6746   $75.67   $75.65   $75.70  
  Purchase #6 $163.62   6.611%   $174.4369   $174.44   $174.45   $174.40  
  Purchase #7 $181.76   12.690%   $204.8253   $204.83   $204.85   $204.80  
  7 purchase totals = $969.57       $1,070.1313   $1,070.13   $1,070.15   $1,070.00